Rotational and linear parameter measurements using a quadrature continuous wave radar with millimeter wave metamaterials and frequency multiplexing in metamaterial-based sensors

ABSTRACT

A sensor system includes a first metamaterial track mechanically coupled to a rotational shaft configured to rotate about a rotational axis, wherein the first metamaterial track is arranged at least partially around the rotational axis, and wherein the first metamaterial track includes a first array of elementary structures; at least one transmitter configured to transmit a first continuous wave towards the first metamaterial track, wherein the first metamaterial track is configured to convert the first continuous wave into a first receive signal based on a rotational parameter of the rotational shaft; and at least one quadrature continuous-wave receiver configured to receive the first receive signal, acquire a first measurement of a first property of the first receive signal, and determine a measurement value for the rotational parameter of the rotational shaft based on the first measurement.

RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.17/518,912, filed Nov. 4, 2021, which is incorporated herein byreference in its entirety.

BACKGROUND

Vehicles feature numerous safety, body, and powertrain applications thatrely on speed sensing, position sensing, and/or angle sensing. Forexample, in a vehicle's Electronic Stability Program (EPS), magneticangle sensors and linear Hall sensors can be used to measure steeringangle and steering torque. Modern powertrain systems can rely onmagnetic speed sensors for camshaft, crankshaft and transmissionapplications, along with automotive pressure sensors, to achieverequired CO2 targets and smart powertrain solutions. However, adisadvantage of known solutions is that they are sensitive to magneticdisturbances.

Magnetic disturbance fields are prevalent in vehicles such that magneticangle-measurements often have to endure harsh environments. This isespecially problematic in hybrid and electric vehicles, where many wireswith high currents are located near the sensor system. Thus, externalmagnetic disturbance fields may be generated by current-rails in avehicle that influence the accuracy of the magnetic angle measurements.Thus, sensors that are robust against electromagnetic stray fields maybe desirable.

Additionally, multiple sensors are typically required to measuremultiple measurement parameters, such as movement speed (rotational orlinear), movement direction, position, rotation angle, torque, and thelike. Thus, a sensor capable of performing measurements on multiplemeasurement parameters, including performing those measurements inparallel may be desirable.

This sensor systems may require an elaborate solution for signaltransmission and analysis, especially at the correspondingly highfrequencies in the millimeter (mm)-wave regime. Availablefrequency-modulated continuous-wave (FMCW) chips have the disadvantageof requiring a large chirp bandwidth for small distance measurements.Further, their sampling rate is limited by the chirp duration. Availablecontinuous-wave doppler radar chips are not suitable for measuringsignals from non-moving objects and thus do not allow measurement ofstarting torque. Accordingly, a sensor that can provide a robust, lowpower, and low-cost system for metamaterial-based mm-wave static ordynamic measurements, including torque, using a quadraturecontinuous-wave (QCW) radar may be desirable. QCW radar is scalable overa broad range of working frequencies, from a few GHz to several hundredGHz.

SUMMARY

One or embodiments provide a sensor system, including: a firstmetamaterial track mechanically coupled to a rotational shaft configuredto rotate about a rotational axis, wherein the first metamaterial trackis arranged at least partially around the rotational axis, and whereinthe first metamaterial track includes a first array of elementarystructures; at least one transmitter configured to transmit a firstcontinuous wave towards the first metamaterial track, wherein the firstmetamaterial track is configured to convert the first continuous waveinto a first receive signal based on a rotational parameter of therotational shaft; and at least one quadrature continuous-wave receiverconfigured to receive the first receive signal, acquire a firstmeasurement of a first property of the first receive signal, anddetermine a measurement value for the rotational parameter of therotational shaft based on the first measurement.

One or more embodiments provide a method of determining a rotationalparameter of a rotatable shaft. The method includes transmitting a firstcontinuous wave towards a first metamaterial track mechanically coupledto the rotatable shaft; converting, by the first metamaterial track, thefirst continuous wave into a first receive signal based on a real-timevalue of the rotational parameter; receiving, by a quadraturecontinuous-wave receiver, the first receive signal; acquiring, by thequadrature continuous-wave receiver, a first measurement of a firstproperty of the first receive signal; and determining, by the quadraturecontinuous-wave receiver, determine the real-time value of therotational parameter of the rotational shaft based on the firstmeasurement.

One or embodiments provide a rotation sensor system, including: arotational shaft configured to rotate about a rotational axis; a firstarray of millimeter-wave (mm-wave) structures mechanically coupled tothe rotational shaft, wherein the first array of mm-wave structures isarranged at least partially around the rotational axis, and wherein thefirst array of mm-wave structures has a first working resonancefrequency; a second array of mm-wave structures mechanically coupled tothe rotational shaft, wherein the second array of mm-wave structures isarranged at least partially around the rotational axis, and wherein thesecond array of mm-wave structures has a second working resonancefrequency that is different from the first working resonance frequency;at least one transmitter configured to transmit a first electro-magnetictransmit signal towards the first array of mm-wave structures andtransmit a second electro-magnetic transmit signal towards the secondarray of mm-wave structures, wherein the first array of mm-wavestructures is configured to convert the first electro-magnetic transmitsignal into a first electro-magnetic receive signal, wherein the secondarray of mm-wave structures is configured to convert the secondelectro-magnetic transmit signal into a second electro-magnetic receivesignal; and at least one receiver configured to receive the firstelectro-magnetic receive signal and the second electro-magnetic receivesignal, determine a first rotational parameter of the rotational shaftbased on the first electro-magnetic receive signal, and determine asecond rotational parameter of the rotational shaft based on the secondelectro-magnetic receive signal, wherein the first rotational parameterand the second rotational parameter are different rotational parameters.

One or embodiments provide a rotation sensor system, including: arotational shaft configured to rotate about a rotational axis; a firstarray of millimeter-wave (mm-wave) structures mechanically coupled tothe rotational shaft, wherein the first array of mm-wave structures isarranged at least partially around the rotational axis, and wherein thefirst array of mm-wave structures has a first working resonancefrequency; a second array of mm-wave structures mechanically coupled tothe rotational shaft, wherein the second array of mm-wave structures isarranged at least partially around the rotational axis, and wherein thesecond array of mm-wave structures has a second working resonancefrequency that is different from the first working resonance frequency;a transmitter configured to transmit an electro-magnetic transmit signaltowards the first array of mm-wave structures and the second array ofmm-wave structures, wherein the first array of mm-wave structures isconfigured to convert the electro-magnetic transmit signal into a firstelectro-magnetic receive signal and the second array of mm-wavestructures is configured to convert the electro-magnetic transmit signalinto a second electro-magnetic receive signal; and at least one receiverconfigured to receive the first electro-magnetic receive signal and thesecond electro-magnetic receive signal, determine a first rotationalparameter of the rotational shaft based on the first electro-magneticreceive signal, and determine a second rotational parameter of therotational shaft based on the second electro-magnetic receive signal,wherein the first rotational parameter and the second rotationalparameter are different rotational parameters.

One or embodiments provide a linear movement sensor system, including: alinear movable target object configured to move linearly in a linearmoving direction; a first array of millimeter-wave (mm-wave) structurescoupled to the linear movable target object, wherein the first array ofmm-wave structures extends along the linear moving direction, andwherein the first array of mm-wave structures has a first workingresonance frequency; a second array of mm-wave structures coupled to thelinear movable target object, wherein the second array of mm-wavestructures extends along the linear moving direction, and wherein thesecond array of mm-wave structures has a second working resonancefrequency that is different from the first working resonance frequency;at least one transmitter configured to transmit at least oneelectro-magnetic transmit signal towards the first array of mm-wavestructures and the second array of mm-wave structures, wherein the firstarray of mm-wave structures is configured to convert one of the at leastone electro-magnetic transmit signal into a first electro-magneticreceive signal and the second array of mm-wave structures is configuredto convert one of the at least one electro-magnetic transmit signal intoa second electro-magnetic receive signal; and at least one receiverconfigured to receive the first and the second electro-magnetic receivesignals, determine a first linear movement parameter of the linearmovable target object based on the first electro-magnetic receivesignal, and determine a second linear movement parameter of the linearmovable target object based on the second electro-magnetic receivesignal, wherein the first linear movement parameter and the secondlinear movement parameter are different linear movement parameters.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments are described herein making reference to the appendeddrawings.

FIG. 1 illustrates a plurality of possible elementary structuresaccording to one or more embodiments;

FIGS. 2A and 2B illustrate a segment of a mm-wave metamaterial trackaccording to one or more embodiments;

FIGS. 3A-3G show different arrangements or patterns of elementarystructures of a metamaterial according to one or more embodiments;

FIG. 4A is a schematic view of an angle sensor system according to oneor more embodiments;

FIG. 4B is a schematic view of an angle sensor system according to oneor more embodiments;

FIG. 5A is a schematic view of a torque measurement system according toone or more embodiments;

FIG. 5B is a schematic view of another torque measurement systemaccording to one or more embodiments;

FIG. 5C is a schematic view of another torque measurement systemaccording to one or more embodiments;

FIG. 6 is a block diagram that illustrates structure of one example of atransceiver according to one or more embodiments;

FIG. 7 illustrates a resonance of a first metamaterial array and aresonance of a second metamaterial array, where the two metamaterialarrays have different working resonance frequencies, according to one ormore embodiments;

FIG. 8 shows a nested arrangement of two metamaterial arrays accordingto one or more embodiments;

FIGS. 9A-9F illustrate cross-sectional views of different possibletransceiver or transmitter/receiver implementations for differentarrangements of metamaterial arrays according to one or moreembodiments;

FIGS. 10A and 10B illustrate a cross-section view and a plan view,respectively, of a linear position sensor system according to one ormore embodiments;

FIG. 11 illustrates a schematic block diagram of a QWC radar transceiveraccording to one or more embodiments; and

FIG. 12 illustrates an example transmission spectra from a metamaterialarray or a mutually coupled pair of metamaterial arrays using twodifferent transmission frequencies according to one or more embodiments.

DETAILED DESCRIPTION

In the following, details are set forth to provide a more thoroughexplanation of the exemplary embodiments. However, it will be apparentto those skilled in the art that embodiments may be practiced withoutthese specific details. In other instances, well-known structures anddevices are shown in block diagram form or in a schematic view ratherthan in detail in order to avoid obscuring the embodiments. In addition,features of the different embodiments described hereinafter may becombined with each other, unless specifically noted otherwise.

Further, equivalent or like elements or elements with equivalent or likefunctionality are denoted in the following description with equivalentor like reference numerals. As the same or functionally equivalentelements are given the same reference numbers in the figures, a repeateddescription for elements provided with the same reference numbers may beomitted. Hence, descriptions provided for elements having the same orlike reference numbers are mutually exchangeable.

In this regard, directional terminology, such as “top”, “bottom”,“below”, “above”, “front”, “behind”, “back”, “leading”, “trailing”,etc., may be used with reference to the orientation of the figures beingdescribed. Because parts of embodiments can be positioned in a number ofdifferent orientations, the directional terminology is used for purposesof illustration. It is to be understood that other embodiments may beutilized and structural or logical changes may be made without departingfrom the scope defined by the claims. The following detaileddescription, therefore, is not to be taken in a limiting sense.Directional terminology used in the claims may aid in defining oneelement's spatial or positional relation to another element or feature,without being limited to a specific orientation.

It will be understood that when an element is referred to as being“connected” or “coupled” to another element, it can be directlyconnected or coupled to the other element or intervening elements may bepresent. In contrast, when an element is referred to as being “directlyconnected” or “directly coupled” to another element, there are nointervening elements present. Other words used to describe therelationship between elements should be interpreted in a like fashion(e.g., “between” versus “directly between,” “adjacent” versus “directlyadjacent,” etc.).

In embodiments described herein or shown in the drawings, any directelectrical connection or coupling, i.e., any connection or couplingwithout additional intervening elements, may also be implemented by anindirect connection or coupling, i.e., a connection or coupling with oneor more additional intervening elements, or vice versa, as long as thegeneral purpose of the connection or coupling, for example, to transmita certain kind of signal or to transmit a certain kind of information,is essentially maintained. Features from different embodiments may becombined to form further embodiments. For example, variations ormodifications described with respect to one of the embodiments may alsobe applicable to other embodiments unless noted to the contrary.

The terms “substantially” and “approximately” may be used herein toaccount for small manufacturing tolerances (e.g., within 5%) that aredeemed acceptable in the industry without departing from the aspects ofthe embodiments described herein. For example, a resistor with anapproximate resistance value may practically have a resistance within 5%of that approximate resistance value.

In the present disclosure, expressions including ordinal numbers, suchas “first”, “second”, and/or the like, may modify various elements.However, such elements are not limited by the above expressions. Forexample, the above expressions do not limit the sequence and/orimportance of the elements. The above expressions are used merely forthe purpose of distinguishing an element from the other elements. Forexample, a first box and a second box indicate different boxes, althoughboth are boxes. For further example, a first element could be termed asecond element, and similarly, a second element could also be termed afirst element without departing from the scope of the presentdisclosure.

One or more aspects of the present disclosure may be implemented as anon-transitory computer-readable recording medium having recordedthereon a program embodying methods/algorithms for instructing theprocessor to perform the methods/algorithms. Thus, a non-transitorycomputer-readable recording medium may have electronically readablecontrol signals stored thereon, which cooperate (or are capable ofcooperating) with a programmable computer system such that therespective methods/algorithms are performed. The non-transitorycomputer-readable recording medium can be, for example, a CD-ROM, DVD,Blu-ray disc, a RAM, a ROM, a PROM, an EPROM, an EEPROM, a FLASH memory,or an electronic memory device.

One or more elements of the present disclosure may be configured byimplementing dedicated hardware or a software program on a memorycontrolling a processor to perform the functions of any of thecomponents or combinations thereof. Any of the components may beimplemented as a central processing unit (CPU) or other processorreading and executing a software program from a recording medium such asa hard disk or a semiconductor memory device. For example, instructionsmay be executed by one or more processors, such as one or more CPUs,digital signal processors (DSPs), general-purpose microprocessors,application-specific integrated circuits (ASICs), field programmablelogic arrays (FPGAs), programmable logic controller (PLC), or otherequivalent integrated or discrete logic circuitry.

Accordingly, the term “processor,” as used herein refers to any of theforegoing structures or any other structure suitable for implementationof the techniques described herein. A controller including hardware mayalso perform one or more of the techniques of this disclosure. Acontroller, including one or more processors, may use electrical signalsand digital algorithms to perform its receptive, analytic, and controlfunctions, which may further include corrective functions. Suchhardware, software, and firmware may be implemented within the samedevice or within separate devices to support the various techniquesdescribed in this disclosure.

A signal processing circuit and/or a signal conditioning circuit mayreceive one or more signals (i.e., measurement signals) from one or morecomponents in the form of raw measurement data and may derive, from themeasurement signal further information. Signal conditioning, as usedherein, refers to manipulating an analog signal in such a way that thesignal meets the requirements of a next stage for further processing.Signal conditioning may include converting from analog to digital (e.g.,via an analog-to-digital converter), amplification, filtering,converting, biasing, range matching, isolation and any other processesrequired to make a signal suitable for processing after conditioning.

It will be appreciated that the terms “sensor”, “sensor element”, and“sensing element” may be used interchangeably throughout thisdescription, and the terms “sensor signal” and “measurement signal” mayalso be used interchangeably throughout this description.

Embodiments are discussed below in the context of a millimeter wave(mm-wave) sensor and mm-wave systems that include a mm-wave transmitter,a mm-wave receiver, and/or a mm-wave transceiver. Mm-waves are radiowaves designated in the band of radio frequencies in the electromagneticspectrum from 30 to 300 gigahertz (GHz) and may also be used as radarwaves. Thus, a mm-wave sensor, system, transmitter, receiver, ortransceiver described herein may also be regarded to as a radar sensor,system, transmitter, receiver, or transceiver, and a mm-wave may beregarded to as a radar signal. It should be noted, however, that theembodiments may also be applied in applications different from radarsuch as, for example, radio frequency (RF) transmitters, receivers, ortransceivers of RF communication devices. In fact, any RF circuitry maytake advantage of the concepts described herein. A mm-wave sensor ormm-wave system may be configured as an angle sensor, a linear positionsensor, a speed sensor, a motion sensor, and the like.

A metamaterial is a material engineered to have a property that is notfound in naturally occurring materials. They are made from assemblies ofmultiple structural elements fashioned from composite materials such asmetals or plastics. The materials may be arranged in repeating orperiodic patterns, at scales that are smaller than the wavelengths ofthe phenomena they influence. In other words, metamaterials attain thedesired effects by incorporating structural elements of sub-wavelengthsizes, i.e., features which are actually smaller than the wavelength ofthe electromagnetic waves that they affect.

As a result, metamaterials derive their properties not necessarily fromthe properties of the base materials, but from their designedstructures. Their precise shape, geometry, size, orientation, andarrangement of the structural elements gives the metamaterials theirsmart properties capable of manipulating electromagnetic waves: byblocking, reflecting, absorbing, enhancing, or bending waves, to achievebenefits. Thus, a metamaterial is defined as an artificial compositethat gains its electrical properties from its exactingly-designedstructures and their arrangement rather than inheriting them directlyfrom which the materials it is composed.

A metamaterial may be a subset of a larger group of heterogeneousstructures consisting of a base solid material and elements of adifferent material. The distinction of metamaterials is that they havespecial, sometimes anomalous, properties over a limited frequency band.For example, mm-wave metamaterials may exhibit special properties over amillimeter band, which is the band of spectrum between 30 GHz and 300GHz noted above.

In the context of the described embodiments, a metamaterial is atwo-dimensional (2D) or three-dimensional (3D) array of elementarystructures, which are coupled to each other. “Elementary structures,” asused herein, may be referred to as discrete structures, elementstructures, or a combination thereof. In some cases, the elementarystructures may be referred to simply as “structures.”

The overall array provides macroscopic properties, which can be designedby the used elementary structures and their coupling paths.Metamaterials are configured for different kind of waves likeelectromagnetic waves (e.g., optical, infrared (IR), and mm-waves) andmechanical waves (e.g., ultrasonic). The scale of the elementarystructures and their grid pitch scale with the wavelength of the targetfrequency range.

Elementary structures in mm-wave metamaterials may includeresonator-elements, antenna-elements, filter-elements,waveguide-elements, transmission line elements, or a combination ofthose shown in FIG. 1 . The elementary structure size may range up toseveral wavelengths but is typically below one wavelength. They consistof parts that generate magnetic fields (e.g., conductor rings) and otherparts that create electrical fields (e.g., gaps between conductors).Furthermore, they also may have elements that have electromagnetic waveproperties, such as a short transmission line segment.

In general, those elementary structures electrically representresistive-inductive-capacitive (RLC) networks. In the frequency rangewhere they will be used in the meta material, the characteristic oftheir resistive, inductive, and capacitive parameters is distributedover the geometry. Since filters, resonators, transmission lines, andantennas can be differently parametrized representatives of identicalstructures it is often not unambiguously possible to assign a structureto a single group. Thus, it is to be understood that a structuredescribed as resonator can also be seen as antenna or a filter dependingon its use or implementation details. Furthermore, the behavior may alsochange with the frequency where it is operated and a structure thatbehaves as transmission line for one frequency may also expose a filtercharacteristic or create a resonance at another frequency of operation.Finally, the choice of the material impacts the behavior which meansthat a choice of a better conductor will emphasize a resonant behaviorwhile a less conductive material will increase the damping and make afilter characteristic dominant.

FIG. 1 illustrates a plurality of possible elementary structuresaccording to one or more embodiments. The elementary structures 1include a split ring resonator 2 having one capacitor coupling 2 a, asplit ring resonator 3 having two capacitor couplings 3 a and 3 b, asplit ring resonator 4 having four capacitor couplings 4 a-4 d, antennastructure 5, an antenna coil 6, a nested split ring resonator 7, antennastructure 8, antenna structure 9, antenna structure 10, transmissionline structure 11, antenna structure 12, coupled split ring resonators13, split ring resonator 14, partial ring or coupling structure 15, andcoupled split ring resonator 16.

The transmission line structure 11 may be a damping structure or delaystructure. It may be used in an alternating configuration withresonators in order to establish an attenuated or phase shifted couplingbetween them instead of coupling directly. Coupling to the resonatorscan be capacitive or galvanic. It may also extend onto a second layer,for example, with an identical structure creating a real transmissionline (i.e., two parallel wires).

The partial ring or coupling structure 15 may be referred to as apartial ring structure in the context of it being half of a split ringresonator 18. In this context, the partial ring structure 15 is coupledto a second layer to form a resonator. The partial ring or couplingstructure 15 may also be used as a coupling structure as in the examplein FIG. 3B. In this context, it provides capacitive coupling betweenring resonator elements, but will not resonate remarkably (at least atthe low frequency) as the coupled split ring resonators.

Furthermore, the elementary structures can be three-dimensional as well,such as spiral coils and nested split ring resonators that are orientedinto all three Cartesian coordinate directions. Furthermore,three-dimensional structures can be generated by layeringtwo-dimensional elementary structures in a stacked arrangement. Forexample, two elementary structures may be layered over one another in avertical dimension so that they overlap with each other. In this way, avertical capacitive coupling may be achieved between the two elementarystructures and may be adjusted by varying an amount of overlap in ahorizontal dimension.

FIG. 1 further illustrates a stacked split ring resonator structure 17having three split ring resonators stacked on top of each other. Thestacked split ring resonator structure 17 may be formed by using threemetallization layers stacked on top of each other. FIG. 1 furtherillustrates a split ring resonator 18 made of two half-ring structures15 that overlap such that a vertical capacitive coupling exists betweenthe two half-ring structures. By varying the amount of overlap, the loopsize can be made larger (e.g., by decreasing the amount of overlap) orsmaller (e.g., by increasing the amount of overlap), which in turnresults in a lower vertical capacitive coupling or a higher verticalcapacitive coupling, respectively.

In order to achieve a quasi-homogeneous macroscopic behavior, theelementary structures are arranged in arrays which typically havedimensions that are larger than a wavelength of the target frequencyrange and include a multitude of elementary structures in each utilizeddirection.

FIGS. 2A and 2B illustrate a segment of a mm-wave metamaterial trackaccording to one or more embodiments. A mm-wave metamaterial track is astripe of mm-wave metamaterial that has multiple elementary structuresarranged in both widthwise (axial) and lengthwise (rotational)dimensions. Here, the direction orthogonal to a rotation direction maybe referred to as an axial direction.

Specifically, FIG. 2A shows an example of a 2D array 20 of split ringresonators, which are expected to extend further in both horizontal androtational (circumferential) directions. However, it will be appreciatedthat the split ring resonators may be exchanged with any type ofelementary structure, for example, with any of those shown in FIG. 1 .Each split ring resonator comprises an open ring that represents aninductivity (L) and a gap or opening that provides a capacitive coupling(C). Thus, each split ring resonator is a type of LC resonator.

The elementary structures that make up the segment of a mm-wavemetamaterial track shown in FIG. 2A have a fixed arrangement or fixedproperty along the rotation direction. For example, the split ringresonators in each row are arranged in the same position andorientation. Furthermore, the spacing between adjacent split ringresonators in the rotation direction is fixed along the track. As such,array 20 does not have any change in property of the metamaterialstructures along the track in the rotation direction. One or moreproperties between the structures, such as spacing and orientation, maychange in the axial direction as long as each row of structures has thesame pattern.

There exists a mutual coupling of the structures in the array 20, whichcan be a capacitive coupling, an inductive coupling, or both. In thiscase, both types of coupling is present. For example, capacitivecoupling between structures exists in the vertical direction (i.e.,along the rotation direction) on the sides where rings are closetogether. In addition, inductive coupling between structures is providedby the field generated by each split ring resonator.

Thus, electrically, the arrangement of the elementary structures in anarray introduces a mutual coupling between the elementary structures,wherein the coupling effect may utilize electric field (capacitive nearfield coupling), magnetic field (inductive near field coupling),waveguide coupling, or electromagnetic waves (far field coupling). Dueto the dimensions of the arrays and depending on the type of usedelementary structures, the coupling effect will typically made up of amixture of all mechanisms.

The manner in which the structures are coupled affects the couplingbehavior of the array or a portion of that array. In turn, this couplingbehavior impacts an effect the individual structures or a group ofstructures have on a transmission wave or signal incident on thatstructure or that group of structures.

Furthermore, the coupling effect between structures is different if gapsor openings of neighboring structures are face-to-face or if the gapsface (i.e., are adjacent to) a closed segment of a neighboringstructure. For example, FIG. 2B shows an example of 2D array 21 of splitring resonators in which an orientation of the split ring resonatorschanges in both the horizontal (width) and vertical (length) directionsof the array 21 (i.e., of the metamaterial track). In other words, thelocation of the gap of each split ring resonator varies acrossneighboring structures and the rows of structures have differentpatterns. Here, while not required, it is possible that each row ofstructures has a unique pattern. As a result, the coupling effectbetween structures in FIG. 2B is different than the coupling effectproduced by the structures shown in FIG. 2A.

Furthermore, the coupling effect between structures in FIG. 2B changespartially along the array in the rotation direction, whereas thecoupling effect between structures in FIG. 2A does not change along thearray in the rotation direction. The different shapes (circular versusrectangular) may also impact the characteristic of the structure itselfand the coupling effect.

Each elementary structure has a size (e.g., a width or diameter) of 10%to 100% of the wavelength of a transmitted mm-wave to which thestructure is sensitive. The array 20 may be a single metallization layerdisposed or printed on a film such that the array 20 is two-dimensional.As noted above, it may also be possible to stack multiple metallizationlayers to form a 3D array.

Thus, arrays of elementary structures described herein include multiplerepetitions of element structures having same or differing arrangementswith respect to each other that induce a property on a transmission waveor signal incident thereon due to the coupling effect between thestructures. As will be seen in FIGS. 3A-3G, at least one propertychanges along the array in the rotation direction which causes at leastone coupling effect between elementary structures of the array to changecontinuously along the array in the rotation direction. This may allow,for example, to determine a rotational position change and/or arotational angular position of the array. In contrast, for array 20, theproperties are fixed along the array in the rotation direction such thatthe coupling effects between elementary structures of the array do notchange and remain fixed along the array in the rotation direction.

As will become apparent in the following description, one or moremm-wave metamaterial tracks may also be used to perform torquemeasurements and/or off-axis angle measurements pertaining to arotatable target object.

A mm-wave metamaterial track may be provided on a target object suchthat it forms a closed loop around an axis of rotation, thereby forminga 360° periodical pattern. In this way, a target object is a carrierstructure for a mm-wave metamaterial track to be disposed. For example,the elementary structures of an array may have a 360° periodical patternthat may change continuously or in discrete steps around thecircumference or along the perimeter of the metamaterial track. Forexample, tracks used for direct torque measurement may not have anychange in property of the metamaterial structures along the track in therotational direction, such as the case for array 20. In contrast, tracksused for angle measurement, rotational position change, rotationalspeed, rotational direction, or indirect torque measurement may changein property of the metamaterial structures along the track in therotational direction, such as the case for those tracks shown in FIGS.3A-3G. If the pattern changes, it may do so by having a periodic changealong the closed-loop of the metamaterial track from 0° to 360°, andthen repeat. In some cases, the pattern may change multiple times from0° to 360°, giving multiple periodic changes along the metamaterialtrack. The pattern change may be made in incrementally (e.g.,row-by-row) within the array of elementary structures such that thechange is continuous.

There are diverse possibilities for changing a metamaterial propertyaccording to a 360° periodical pattern. It will also be appreciated thata rotational segment of less than 360° may also be applicable. Forexample, applications that measure limited angle ranges (e.g., throttlevalve, chassis level, gas pedal) may also be used. In these cases, thetarget pattern need not be 360° periodic and can simply change thepattern from a minimum value to a maximum value over the used anglerange (e.g., 45°, 60°, 90°, 180° etc.). It naturally follows that thetarget object also does not need to be a complete disc and can bereduced to a segment.

A property and/or arrangement of the metamaterial may be specific to anabsolute angular position along the metamaterial track, and, thus, isalso specific to an absolute angular position of the rotatable targetobject. An absolute angular position is an angular position relative toa predetermined (i.e., reference) angular position of the rotatabletarget object. For example, the reference angular position may be zerodegrees, and an absolute angular position may a specific positionrotated from zero degrees over a 360° period. Thus, each absoluteangular position has an absolute angular value from 0° to 360°.

The following different variations may be used to change the behavior ofmetamaterial along the perimeter of a metamaterial track. Thus, FIGS.3A-3G show different arrangements or patterns of elementary structuresof a metamaterial according to one or more embodiments. These tracks maybe used for angle measurement of a corresponding carrier substrate, arotational position change of a corresponding carrier substrate, or anindirect torque measurement of a torque applied to a rotatable shaft.

FIG. 3A is a schematic diagram of an array of elementary structures 301of a metamaterial track according to one or more embodiments. Here, thearray includes multiple rows of split ring resonators 31 a-34 a in whichthe structures in each row have a same configuration and orientation.However, the structures in different rows have different configurations.

A 360° periodical pattern may be used to change the coupling capacitanceof the split ring resonators along the rotation direction. For example,the coupling capacitance may be increased (or decreased) in thedirection of rotation. Here, this is achieved by increasing (ordecreasing) the length of the lines inside the opening of the split ringresonator, which results in a gradual and continuous increase (ordecrease) in coupling capacitance in the rotation direction. This changein coupling capacitance along the rotation direction (i.e., along theperimeter of the metamaterial track) shifts the resonance frequency suchthat the change in the phase shift or the amplitude of a receive signalwith respect to the transmit signal can be measured. Each phase shiftvalue or amplitude value is specific to an absolute angular position(i.e., an angular value) of the rotatable target object.

FIG. 3B is a schematic diagram of an array of elementary structures 302of a metamaterial track according to one or more embodiments. Here, thearray includes multiple rows of split ring resonators 31 b-34 b in whichthe structures in each row have a same configuration and orientation.However, the structures in different rows have different orientations.

Thus, on the surface of the target object, the split ring resonators 31b-34 b are rotated or pivoted (e.g., clockwise or counterclockwise)incrementally in varying degrees along the rotation direction. As aresult, the structures in each row have a different angled orientationwith respect to structures in neighboring rows, resulting in a gradualand continuous increase (or decrease) in coupling capacitance in therotation direction. This makes the metamaterial sensitive to apolarization of the mm-wave, and, specifically changes the sensitivityto the electrical field component of the transmitted wave that changesalong the rotation direction. Here, an influence on the polarization isrealized since the direction of the dominant E Field in the gap ischanging. Thus, a shift in polarization may be measured that is specificto the absolute angular position (i.e., an angular value) of therotatable target object.

FIG. 3C is a schematic diagram of an array of elementary structures 303of a metamaterial track according to one or more embodiments. Here, thearray includes multiple rows of split ring resonators 31 c in which thestructures in throughout the array have a same configuration andorientation.

Here, the mutual capacitive coupling of the structures is gradually andcontinuously changed in the rotation direction by increasing ordecreasing the distances d1, d2, d3, and so on between structures alongthe rotation direction. Thus, rows at the top are closer together thanthe rows at the bottom of the array. This scales the capacitance betweenstructures in way that is periodical over 360°.

FIG. 3D is a schematic diagram of an array of elementary structures 304of a metamaterial track according to one or more embodiments. Here, thearray includes multiple rows of split ring resonators 31 d-34 d in whichthe structures in each row have a same configuration and orientation.However, the structures in different rows have different configurations.

In this case, an inductive coupling scaled by reducing or increasing theloop area in along the rotation direction. For example, the loop size ofconsecutive rows gradually changes along the rotation direction. Thus,the loop size of the split ring resonators 31 d is larger than the loopsize of the split ring resonators 32 d, which is larger than the loopsize of the split ring resonators 33 d, and so on. This also results ina change in the spacing between structures in the directionperpendicular to the rotation direction, which may further change thecapacitive coupling. This scales the inductive coupling and/or thecapacitive coupling between structures in way that is periodical over360°.

FIG. 3E is a schematic diagram of an array of elementary structures 305of a metamaterial track according to one or more embodiments. Here, thearray includes multiple rows of split ring resonators 31 e in which thestructures in throughout the array have a same configuration andorientation. However, the density of the structures is changed in therotation direction by gradually and continuously increasing ordecreasing the density of the structures along the rotation direction.

For example, each successive row of structures may be populated moredensely or less densely than a preceding row of structures. For example,every position in a first row may be occupied by a structure making up afirst (full) density of structures in that row. In a second row, lessthan every position is occupied by a structure making up a seconddensity of structures in that row that is less dense than the firstdensity. In a third row, less than every position is occupied by astructure making up a third density of structures in that row that isless dense than the second density, and so on. This scales the inductivecoupling and/or the capacitive coupling between structures in way thatis periodical over 360°.

FIG. 3F is a schematic diagram of an array of elementary structures 306of a metamaterial track according to one or more embodiments. Here, thearray includes multiple rows of split ring resonators 31 f in which thestructures in throughout the array have a same configuration andorientation. However, the density of the structures is changed in therotation direction by gradually and continuously increasing ordecreasing the density of the structures along the rotation direction.

In this example, a lateral distance between structures in eachsuccessive row may be changed in the rotation direction by increasing ordecreasing the spacing between structures along the rotation direction.For example, every position in a first row may be occupied by astructure making up a first (full) density of structures in that row. Ina second row, the spacing between adjacent structures is increased incomparison to the spacing between adjacent structures in the first row,making up a second density of structures in that row that is less densethan the first density. In a third row, the spacing between adjacentstructures is increased in comparison to the spacing between adjacentstructures in the second row, making up a third density of structures inthat row that is less dense than the second density, and so on.

FIG. 3G is a schematic diagram of an array of elementary structures 307of a metamaterial track according to one or more embodiments. Here, thearray is a heterogeneous array of mixed different structures such thatthe structure types that populate the array is varied in differentarrangements throughout the array. In this case, two different types ofstructures 31 g and 32 g are use in a pattern that gradually andcontinuously changes the inductive coupling and/or the capacitivecoupling between structures in way that is periodical over 360°. It willbe appreciated that two or more types of structures may also be used toform the heterogeneous array.

In view of the above examples, scaling of a metamaterial property isdone with a pattern of structures that repeats or changes completely andcontinuously around the circumference of the rotatable target or alongthe perimeter of the metamaterial track such that a change inreflectivity and/or transmittivity follows a 360° periodical patternwhere the reflectivity and/or transmittivity is unique for each discreteangle.

FIG. 4A is a schematic view of an angle sensor system 400 according toone or more embodiments. The angle sensor system 400 includes arotatable target object 40 configured to rotate about an axis ofrotation 41 (i.e., a rotational axis). The rotatable target object 40may be a disc or a wheel coupled to a shaft 42 that extends along therotational axis 41. As the shaft 42 rotates, so does the rotatabletarget object 40. The rotatable target object 40 represents a mechanicaltarget for one or more mm-wave beams.

The rotatable target object 40 includes two mm-wave metamaterial tracks43 and 44 that each form a closed loop around the shaft 42. In thisexample, the two mm-wave metamaterial tracks 43 and 44 are concentricloops located at different distances from the rotational axis. In someembodiments, it may be possible to use a single closed-loop metamaterialtrack or more than two closed-loop metamaterial tracks. The mm-wavemetamaterial tracks 43 and 44 are fixed to the rotatable target object40 such that they co-rotate with the rotatable target object 40 as itrotates.

It may also be possible to use tracks with different characteristic ofthe variations of the patterns, for example, implementing a sinefunction or a cosine function in the varying parameter of themetamaterial. Furthermore, reference tracks that do not change thecharacteristic of the meta material may be of interest to characterizethe influence of environmental influences or setup parameters like thedistance between the antenna and the meta material stripe or thetemperature and humidity of the ambient environment. Multiple referencestripes with different metamaterial setups may be used to deliverdifferent reference measurements. For example, different referencestripes may be used to provide for a minimum and a maximum of thevariation of metamaterial properties.

The angle sensor system 400 further includes a transceiver TRX 45configured to transmit and receive mm-waves. In particular, thetransceiver 45 includes a transmitter antenna 46 configured to transmita mm-wave beam (i.e., an electro-magnetic transmit signal) at the twometamaterial tracks 43 and 44. The transmitter antenna 46 may be furtherrepresentative of multiple antennas or an antenna array. For example, inorder to achieve a homogeneous radiation on each metamaterial track,multiple transmitter antennas or transmitter antenna arrays may be usedsuch that each antenna or antenna array is focused on a different track.In this case, the transmitter antennas can be operated in parallel or byseparate transmitters.

The transceiver 45 also includes two receiver antennas 47 and 48, eachconfigured to receive a partially-reflected mm-wave (i.e., anelectro-magnetic receive signal) from a corresponding metamaterial trackof the two metamaterial tracks 43 and 44. In other words, the tworeceiver antennas 47 and 48 are isolated from each other in a way thatreceiver antenna 47 substantially receives a partially-reflected mm-waveonly from one of the tracks (e.g., metamaterial track 44) and receiverantenna 48 substantially receives a reflected mm-wave only from theother one of the tracks (e.g., metamaterial track 43). Thus, isolationsbetween the antennas or between the tracks, such as a metal stripe, maybe provided.

While a small portion of a non-corresponding reflected mm-wave may bereceived at each antenna 47 and 48, this signal may be attenuated to theextent that the signal can be ignored or filtered out as noise by thetransceiver 45.

In addition, it will be appreciated that the transceiver 45 may includetwo transmitter antennas instead of a single transmitter antenna, whereeach transmitter antenna is arranged to target a single metamaterialtrack. Thus, each mm-wave may be exclusively incident on a correspondingtrack. Alternatively, a transmitter antenna may target two or moretracks, where the mm-wave is exclusively incident on the correspondingtracks. Thus, different groups of tracks may be targeted by differenttransmitter antennas.

It will further be appreciated that two transceivers, one for eachmetamaterial track, can be used. It will further be appreciated that tworeceiver and transmitter pairs, one for each metamaterial track, can beused instead of one or more transceivers. It may also be implemented ina way where one antenna is used as a transmit and receive antenna and asplitter separates energy transmission paths (e.g., a rat-race coupleror a hybrid ring coupler) in the RF part. The splitter is configured todirect the received wave from the antenna to the receiver while itdirects the transmit signal from the transmitter to the antenna fortransmission.

Regardless of the configuration, it will be understood that at least onetransmitter and at least one receiver is implemented for transmittingand detecting mm-wave beams where different receiving antenna andreceiving circuitry correspond to different closed-loop metamaterialtrack on a one-to-one basis. The transmitters and receivers may beelectrically coupled to a system controller and/or a DSP.

FIG. 4B is a schematic view of an angle sensor system 401 according toone or more embodiments. The angle sensor system 401 is similar to theangle sensor system 400 depicted in FIG. 3A, with the exception that theangle sensor system 301 is configured to monitor a mm-wave that passesthrough the two metamaterial tracks 43 and 44 instead of monitoringreflected mm-wave as was the case in FIG. 3A. As a result, angle sensorsystem 301 includes a transmitter including the transmitter antenna 46,and a receiver 45 b, including the receiver antennas 47 and 48. Thereceiver antenna 47 is configured to receive a partially transmittedmm-wave (i.e., an electro-magnetic receive signal) as a result of thetransmitted mm-wave interacting with (i.e., being partially absorbed byand transmitted through) the metamaterial track 44. Similarly, thereceiver antenna 48 is configured to receive a partially transmittedmm-wave (i.e., an electro-magnetic receive signal) as a result of thetransmitted mm-wave interacting with (i.e., being partially absorbed byand transmitted through) the metamaterial track 43.

It will also be appreciated that a combination of FIGS. 4A and 4B may berealized. For example, one receiver may be arranged for detecting andmeasuring a partially-reflected mm-wave from one of the metamaterialtracks (i.e., metamaterial track 44) and another receiver may bearranged for detecting and measuring a partially transmitted mm-wavethat passes through the other one of the metamaterial tracks (i.e.,metamaterial track 43). In addition, two receivers may be used foranalyzing a same metamaterial track, where one detects and measures apartially-reflected mm-wave and the other detects and measures apartially-transmitted mm-wave. Accordingly, one metamaterial track maybe configured with higher reflectivity and the other metamaterial trackmay be configured with a higher absorptivity with respect to oneanother.

Based on the embodiments shown in FIGS. 4A and 4B and combinationsthereof, an electro-magnetic transmit signal is converted into anelectro-magnetic receive signal by interacting with a metamaterialtrack. The interaction may include a reflection, an absorption, atransmission, or a combination thereof. Each receiver antenna is coupledto receiver circuitry configured to demodulate a receive signal in orderto determine a characteristic of the receive signal. An absolute angularposition of the rotatable target object 40 is then determined by thereceiver circuit or a system controller utilizing a signal processorbased on the determined characteristic.

In particular, each metamaterial track is configured such that acharacteristic or property of the metamaterial changes along theperimeter of the track. Thus, how the metamaterial interacts with amm-wave changes along the perimeter of the track. For example, theelementary structures of an array have a 360° periodical pattern thatchanges continuously around the circumference of the rotatable targetand/or along the perimeter of the metamaterial track. Thus, the patterncontinuously changes from 0° to 360° along the closed-loop of themetamaterial track, and then repeats. In this way, a property and/orarrangement of the metamaterial (i.e., of the elementary structures) isspecific to an absolute angular position along the metamaterial track,and, thus, is also specific to an absolute angular position of therotatable target object. An absolute angular position is an angularposition relative to a predetermined (i.e., reference) angular positionof the rotatable target object. For example, the reference angularposition may be zero degrees, and an absolute angular position may aspecific position rotated from zero degrees over a 360° period. Thus,each absolute angular position has an absolute angular value from 0° to360°.

More generally, it is possible for the periodical pattern of theelementary structures of an array to have a period of 360°/N, with Nbeing an integer number greater than zero. That is, the periodicalpattern repeats every 360°/N. In this case, multiple predetermined(i.e., reference) angular positions of the rotatable target object maybe known, and each absolute angular position has an absolute angularvalue from one of the reference angular positions. Each referenceangular position is detectable based on the characteristic or propertyof the metamaterial at a specific position along the track. The angularrate of change may also be used to calculate the rotation speed.

The characteristic or property of the metamaterial at a specificposition along the track results an angle-dependent behavior orinteraction with an mm-wave, where the angle-dependent behavior orinteraction is an angle-dependent reflection, angle-dependentabsorption, angle-dependent transmission, or an angle-dependentcombination thereof.

A receiver circuit may receive and demodulate a receive signal, andevaluate an amplitude modulation and/or a phase modulation of thereceive signal using amplitude analysis and/or phase analysis,respectively. For example, the receiver circuit may evaluate anamplitude variation or a phase shift of the receive signal. The receivecircuit may then determine an absolute angular position of themetamaterial track and/or the rotatable target object based on thedetermined amplitude modulation or phase modulation. For example, thereceiver circuit may refer to a look-up table provided in memory thatstores angular positions relative to a specific amplitude modulation orphase modulation.

Thus, either the amplitude or the phase of the received signal isanalyzed with respect to the same property of the transmitted signal.The metamaterial is a passive structure, it cannot the frequency of thesignal. However, it can change its own resonance frequency or, bettersaid, the locations of its poles and zeros, which can then influence thereflected or the transmitted signal and be detected in amplitude andphase or in real and imaginary part of the signal. Both combinationsdescribe the possible influence completely. Analyzing the shift of aresonance or a pole or a zero may also be characterized over thefrequency with a frequency sweep of the transmit signal, but requires amore complex evaluation circuitry.

As an example for determining an absolute angular position or discreteangular value for a given metamaterial track, the transceiver 45 maytransmit a continuous mm-wave as a carrier signal that has a constantfrequency. Each metamaterial track receives the carrier signal andpartially reflects or transmits the signal back at the transceiver 45.The transceiver 45 includes a receiver circuit that includes twodemodulators (e.g., two mixers), each configured to demodulate areceived signal from a corresponding metamaterial track. Alternatively,the receiver circuit may include a multiplexer coupled to singledemodulator that demodulates both received signals in a multiplexedmanner. In any case, the receiver circuit is configured to determine aphase and/or an amplitude of each received signal, and compare thedetermined phase and/or amplitude to the phase and/or amplitude of thecarrier signal, respectively, to derive the absolute angular position ofthe corresponding metamaterial track. A certain change in phase oramplitude relative to the carrier signal (i.e., a phase shift or anamplitude shift) can correspond to the absolute angular position of thecorresponding metamaterial track.

In addition, a phase shift between two receive signals may be analyzedfor determining an absolute angular position. For example, the rotatedpatterns of metamaterial tracks 43 and 44 may be the same but shifted90° (e.g., clockwise or counterclockwise) from each other such thatthere is a 90° phase shift in the extracted signals resultant from thetwo metamaterial tracks after the evaluation of the metamaterialproperty. This means that two metamaterial tracks at the samecorresponding angle of rotation would produce extracted signals that are90° out of phase from each other. This essentially produces a sinemeasurement signal and a cosine measurement signal while the rotatabletarget object is rotating, that when compared to each other identifies aunique angular position.

Alternatively, two receiver antennas can be focused on the samemetamaterial tracks, but spaced 90° apart. In other words, the placementof the two receiver antenna is such that the pattern of the metamaterialat those locations is shifted with respect to each other that results ina 90° phase shift in the extracted signals resultant at those twolocations. Again, this essentially produces a sine wave measurementsignal and a cosine wave measurement signal while the rotatable targetobject is rotating, that when compared to each other identifies a uniqueangular position.

Analyzing a receive signal from a single track may be used to determinethe angular position (i.e., an angular value) of the rotatable targetobject. From this, the rotational speed may also be calculated bydetermining a rate of change in the angular values. Additionally, byobtaining two measurement signals (e.g., two 90° phase shifted signals),a rotation direction of the rotatable target object may also bedetermined.

For example, the rotation direction may be determined at eachzero-crossing or at some other switching threshold of a firstmeasurement signal (e.g., a sine measurement signal or a cosinemeasurement signal). For example, a DSP may determine whether the firstmeasurement signal has a zero-crossing on a falling edge or on a risingedge, and may further analyze the correlation to a negative value orpositive value of a second measurement signal (e.g., the other of thesine measurement signal and the cosine measurement signal).

For example, a negative value of the second measurement signal at afalling edge of the first measurement signal may indicate a firstrotation direction. A positive value of the second measurement signal ata rising edge of the first measurement signal may also indicate thefirst rotation direction. A positive value of the second measurementsignal at a falling edge of the first measurement signal may indicate asecond rotation direction. A negative value of the second measurementsignal at a rising edge of the first measurement signal may alsoindicate the second rotation direction. Since the second measurementsignal is 90° phase shifted to the first measurement signal, thedetermination of rotation direction is less susceptible to error thatmay be cause by external stray fields, biasing noise, and other types ofinterference.

In addition, or in the alternative, the DSP may evaluate the sign of thesecond measurement signal at each zero crossing of the first measurementsignal. If the sign of the second measurement signal alternates betweentwo successive zero crossings (+− or −+), the rotation direction remainsthe same. However, if the sign of the second measurement signal betweentwo successive zero crossings does not alternate, (++ or −−) a directionchange is detected by the DSP.

Alternatively, in cases where sine and cosine are available for thecalculation of the angle, the rotation direction is self-evidentdepending on increase or decrease of the angle value without using aswitching threshold.

The wide range of flavors that metamaterials offer with differentstructures, layers, and mutual coupling could be evaluated based on acomplete measurement of the parameters using a frequency modulatedsignal over the range in which the spectral relevant effects of themetamaterial appear. However, the target applications will provide a lowcost measurement compared to a traditional radar. Thus, the circuiteffort may be minimized and the RX/TX setup will depend on the finalmetamaterial design.

FIG. 5A is a schematic view of a torque measurement system 500 accordingto one or more embodiments. The torque measurement system 500 includes afirst rotatable target object 51 as a first rotatable carrier structureand a second rotatable target object 52 as a second rotatable carrierstructure. Both carrier structures are configured to rotate about anaxis of rotation 53 (i.e., a rotational axis). The rotatable targetobjects 51 and 52 may be a disc or a wheel coupled to a shaft 54 thatextends along the rotational axis 53. As the shaft 54 rotates, so do therotatable target objects 51 and 52. The rotatable target objects 51 and52 represent mechanical targets for one or more mm-wave beams.Additionally, the rotatable target objects 51 and 52 are laterallyseparated from each other by a distance along the shaft 54. Inparticular, they are laterally spaced apart from each other in atransmission direction of mm-wave beams.

Each rotatable target object 51 and 52 includes a mm-wave metamaterialtrack 55 and 56, respectively, that each form a closed loop around theshaft 54. In this regard, each target object 51 and 52 is a carrierstructure for its respective mm-wave metamaterial track. The mm-wavemetamaterial tracks 55 and 56 are fixed to a respective rotatable targetobject 51 or 52 such that they co-rotate with the respective rotatabletarget object 51 or 52 as it rotates. Additionally, the mm-wavemetamaterial tracks have the same size and shape. As such, in a similarmanner regarding the rotatable target objects 51 and 52, themetamaterial tracks 55 and 56 are laterally spaced apart from eachother, and, more particularly, are laterally spaced apart from eachother in a transmission direction of mm-wave beams.

According to at least one embodiment, metamaterial tracks 55 and 56 eachhave an array of structures whose properties do not change in therotation direction, as explained above in reference to FIG. 2A.Furthermore, the two metamaterial tracks 55 and 56 are close enough thatthe two tracks have a mutual coupling with each other that is induced bya field effect (e.g., an electric field coupling, a magnetic fieldcoupling, or an electromagnetic field coupling) thereby forming aresonant multitrack structure (i.e., a mutually coupled structure). Themutual coupling between tracks 55 and 56 results in a torque-dependentbehavior or interaction with an mm-wave where the torque-dependentbehavior or interaction is a torque-dependent reflection, atorque-dependent absorption, a torque-dependent transmission, or atorque-dependent combination thereof.

When the shaft 54 rotates, there is a torque dependent shift in angularposition (i.e., an angular shift) between the two metamaterial tracks 55and 56 due to the torque applied to the shaft 54. This results in atorque dependent shift in the mutual coupling between the twometamaterial tracks 55 and 56. Since multiple of the metamaterialproperties change simultaneously in response to the applied torque,multiple mm-wave parameters of a signal either transmitted, reflected,or emitted by mutually coupled metamaterial tracks will depend on theapplied torque. Two or more mm-wave parameters of a same signal or ofdifferent signals may be evaluated simultaneously to discriminate theapplied torque. Similarly, a single parameter of two or more signals mayalso be evaluated to discriminate the applied torque. Consequently, ameasurement of all relevant variations can be used to improve theunambiguousness of the torque determination.

The torque measurement system 500 further includes a transceiver TRX 45configured to transmit and receive mm-waves, or a transmitter 45 a and areceiver 45 b configured to transmit and receive mm-waves. Thetransmitter 45 a and a receiver 45 b may be placed such that the tworotatable target objects 51 and 52 and, thus, the two tracks 55 and 56,are arranged between the transmitter 45 a and a receiver 45 b.

The transceiver 45 includes a transmitter antenna 46 configured totransmit a mm-wave beam (i.e., an electro-magnetic transmit signal) as awireless electro-magnetic signal focused at the two metamaterial tracks55 and 56. In the case that a separate transmitter 45 a and receiver isused, the transmitter 45 a may be equipped with the transmitter antenna46.

The transceiver 45 also includes a receiver antenna 47 configured toreceive a partially-reflected mm-wave (i.e., an electro-magnetic receivesignal) as a wireless electro-magnetic signal from both metamaterialtracks 55 and 56. It may also be implemented in a way where one antennais used as a transmit and receive antenna and a splitter separatesenergy transmission paths (e.g., a rat-race coupler or a hybrid ringcoupler) in the RF part. The splitter is configured to direct thereceived wave from the antenna to the receiver while it directs thetransmit signal from the transmitter to the antenna for transmission.

In the case that a separate transmitter 45 a and receiver 45 b is used,the receiver 46 a may be equipped with the receiver antenna 47. Here,the torque measurement system 500 is configured to monitor mm-waves thatpass through the two metamaterial tracks 55 and 56 instead of monitoringreflected mm-waves as was the case with the transceiver 45. As a result,the receiver antenna 47 is configured to receive partially transmittedmm-waves (i.e., electro-magnetic receive signals) as a result of thetransmitted mm-wave interacting with (i.e., being partially absorbed byand transmitted through) the metamaterial tracks 55 and 56.

It will further be appreciated that two transceivers, one for eachmetamaterial track, can be used. It will further be appreciated that tworeceiver and transmitter pairs, one for each metamaterial track, can beused instead of one or more transceivers. It may also be implemented ina way where one antenna is used as transmit and receive antenna and asplitter separates energy transmission paths (e.g., a rat-race coupleror a hybrid ring coupler) in the RF part. The splitter is configured todirect the received wave from the antenna to the receiver while itdirects the transmit signal from the transmitter to the antenna fortransmission.

Regardless of the configuration, it will be understood that at least onetransmitter and at least one receiver is implemented for transmittingand detecting mm-wave beams. The transmitters and receivers may beelectrically coupled to a system controller and/or a DSP.

As noted above, the two metamaterial tracks 55 and 56 are close enoughthat the tracks have a mutual coupling (e.g., an electric fieldcoupling, a magnetic field coupling, or an electromagnetic fieldcoupling) with each other thereby forming a resonant structure thatresults in a torque dependent shift of the transmission or thereflection that is caused by the resonant structure. The torquedependent mutual coupling between the metamaterial tracks 55 and 56 maybe capacitive, inductive, or a combination thereof. In the latter case,one type of coupling may be dominant. For example, capacitive couplingbetween the two tracks may be dominant.

As an example, in the case that the two metamaterial tracks 55 and 56are made up of elementary structures 15, the elementary structures 15 ofthe two metamaterial tracks 55 and 56 couple together to form a splitring resonator 18 as an elementary structure having two poles, which isa resonator whose poles are modified by the shift between the two layerscaused by the applied torque. Thus, the mutual coupling characteristicbetween the two tracks 55 and 56 changes based on the rotationaldisplacement the two tracks undergo as a result of the applied torque.As a result, one or more properties (e.g., amplitude and/or phase) ofthe signal emitted from the resonant multitrack structure formed by thetwo tracks changes based on the rotational displacement, which thuschanges based on the applied torque.

In another example, the two metamaterial tracks 55 and 56 are made up ofelementary structures 2, the elementary structures 2 of the twometamaterial tracks 55 and 56 couple together to form a stacked splitring resonator structure 17 having four pols (2 poles for eachelementary structure 2), which is a resonator whose poles are modifiedby the shift between the two layers caused by the applied torque. Thus,the mutual coupling characteristic between the two tracks 55 and 56changes based on the rotational displacement the two tracks undergo as aresult of the applied torque. As a result, one or more properties (e.g.,amplitude and/or phase) of the signal emitted from the resonantmultitrack structure formed by the two tracks changes based on therotational displacement, which thus changes based on the applied torque.

It will be appreciated that other combinations of elementary structuresis possible, forming different types of mutually coupled structures thathave one or more characteristics that change based on the rotationaldisplacement caused by the applied torque.

It is also noted that the mm-wave, being an electromagnetic wave, has anelectrical field component that stimulates the capacitance of ametamaterial track or the resonant multitrack structure and a magneticfield component that stimulates the inductance of a metamaterial trackor the resonant multitrack structure. Each elementary structure reflectsa part of the mm-wave directly, transmits a part of the mm-wavedirectly, and receives a part of the energy and stores it in itsresonance oscillation. The oscillation caused by the transmissionradiates a part of the energy in either direction. Thus, eachmetamaterial track absorbs part of the energy and stores it.Additionally, each metamaterial track eventually emits the energy thathas been absorbed and stored.

The resonant multitrack structure, also referred to as a mutuallycoupled (multitrack) structure, may also be viewed as a single structurethat emits a mm-wave, either as a reflection and/or a transmission, inresponse to the transmitted mm-wave from the transceiver 45 impingingthereon. This emitted wave has a torque dependent property that may beevaluated by the receiver circuit to determine the applied torque. Forexample, a phase shift and/or an amplitude shift of the received signalwith respect to the transmitted mm-wave may be determined and evaluatedto determine the applied torque.

In particular, when the shaft 54 rotates, there is a torque dependentshift in angular position (i.e., an angular shift) between the twometamaterial tracks 55 and 56 due to the torque applied to the shaft 54.For example, the target objects 51 and 52 rotate by different amountsdue to the applied torque. As a result, the absolute angular position ordiscrete angular value corresponding to track 55 is different than theabsolute angular position or discrete angular value corresponding totrack 56, resulting in angular difference or angular shift that isproportional to the applied torque. The coupling effect between tracks55 and 56 is torque-dependent and changes based on their angular shiftresultant from the applied torque. This change in coupling in turnimpacts at least one coupling-dependent property of a signal interactingwith the mutually coupled structure, which can be measured to determinethe applied torque.

A processor at the receiver is configured to receive at least one signalfrom the mutually coupled structure and determine the applied torquebased on one or more evaluated properties of the at least one receivedsignal. The processor may determine the applied torque based on theevaluated property or properties using, for example, a look-up table oran algorithm.

For example, the signal emitted by the mutually coupled structure formedby tracks 55 and 56 may have at least one property or combination ofproperties unique to the angular shift therebetween, and thus unique tothe applied torque. This is referred to as a direct torque measurement.

Alternatively, the processor may receive signals from each track 55 and56 of the mutually coupled structure, determine a torque-dependentabsolute angular position corresponding to each track, determine theangular difference or shift therefrom, and then determine the appliedtorque based on the determined angular difference using, for example, alook-up table or an algorithm. In this case, the tracks 55 and 56 mayhave array structures that vary in the rotation direction, as describedin reference to 3A-3G, so that the angular position of each track can bedetermined. This is referred to as an indirect torque measurement.

As an example for determining an absolute angular position or discreteangular value for a given metamaterial track, the transceiver 45 maytransmit a continuous mm-wave as a carrier signal that has a constantfrequency. Each metamaterial track that receives the carrier signal maypartially reflect the signal back at the transceiver 45. The transceiver45 includes a receiver circuit that includes two demodulators (e.g., twomixers), each configured to demodulate a received signal from acorresponding metamaterial track. Alternatively, the receiver circuitmay include a multiplexer coupled to single demodulator that demodulatestwo received signals in a multiplexed manner. In any case, the receivercircuit is configured to determine a phase and/or an amplitude of eachreceived signal, and compare the determined phase and/or amplitude tothe phase and/or amplitude of the carrier signal, respectively, toderive the absolute angular position of the corresponding metamaterialtrack. A certain change in phase or amplitude relative to the carriersignal (i.e., a phase shift or an amplitude shift) corresponds to theabsolute angular position of the corresponding metamaterial track. It isalso possible for the receiver circuit to match the phase and/oramplitude differences of two received signals (i.e., one from each track55 and 56) directly to the torque without calculating the absoluteangular positions, via a mapping, look-up table, or the like, that mapsdifferential values of phase and/or amplitude to different amounts oftorque (i.e., torque values).

An applied torque for a given mutually coupled structure may bedetermined in a similar manner for a direct torque measurement. Forinstance, the transceiver 45 may transmit a continuous mm-wave as acarrier signal that has a constant frequency at the mutually coupledstructure. The mutually coupled structure that receives the carriersignal may partially reflect the signal back at the transceiver 45. Themutual coupling between two metamaterial tracks of the mutually coupledstructure depends on the applied torque, which is affects a torquedependent property of the reflected signal.

The transceiver 45 includes a demodulator that is configured todemodulate the received signal and a processor that is configured toevaluate a property of the received signal using at least one of phaseanalysis, amplitude analysis, or spectral analysis, and determine theapplied torque based on the evaluated property.

In particular, the processor is configured to determine a phase and/oran amplitude of each received signal, and compare the determined phaseand/or amplitude to the phase and/or amplitude of the carrier signal,respectively, to derive the applied torque. A certain change in phase oramplitude relative to the carrier signal (i.e., a phase shift or anamplitude shift) corresponds to the applied torque.

In summary, the torque measurement system 500 uses two target objects(i.e., two carrier structures) 51 and 52 each with a metamaterialpattern 55 and 56 on their neighboring surfaces. Each carrier structureis fixed to a shaft 54 within a certain distance between the neighboringcarrier structures. If a torque is applied to the shaft 54, the shaft 54winds depending on its thickness and its Young's modulus. The distancebetween the carrier structures is close enough to ensure that the twometamaterial tracks 55 and 56 mutually couple. Depending on the shift ofthe two metamaterial patterns of the two metamaterial tracks, thecoupling effect between the two metamaterial tracks changes. Thiscoupling effect is unique to the amount of applied torque. As a result,the change in the coupling effect causes a property of one or moresignals emitted from the metamaterial tracks 55 and 56 to be altered,which can be measured and analyzed for determining the applied torque.

FIG. 5B is a schematic view of a torque measurement system 501 accordingto one or more embodiments. The torque measurement system 501 is similarto the torque measurement system 500 depicted in FIG. 5A, with theexception that the torque measurement system 401 includes additionalmetamaterial tracks on each rotatable target object 51 and 52. Twometamaterial tracks 55 a and 55 b are attached to rotatable targetobject 51 and two metamaterial tracks 56 a and 56 b are attached torotatable target object 52. The two mm-wave metamaterial tracks 55 a and55 b attached to rotatable target object 51 are concentric loops locatedat different distances from the rotational axis 53. Similarly, the twomm-wave metamaterial tracks 56 a and 56 b attached to rotatable targetobject 52 are concentric loops located at different distances from therotational axis 53.

Furthermore, metamaterial tracks 55 a and 56 a are aligned (i.e., arelocated at the same radial distance from the rotational axis 53) and arein close proximity such that they are mutually coupled. Similarly,metamaterial tracks 55 b and 56 b are aligned (i.e., are located at thesame radial distance from the rotational axis 53) and are in closeproximity such that they are mutually coupled. Thus, two mutuallycoupled structures are formed, where the first one is formed by tracks55 a and 56 a, and the second one is formed by tracks 55 b and 56 b.

In addition, the torque measurement system 401 includes two antennas A1and A2 both configured to transmit and receive mm-wave signals. Here,antenna A1 is aligned with metamaterial tracks 55 a and 56 a, and, assuch, is configured to transmit a mm-wave beam at those mutually coupledtracks and receive reflected signals therefrom. Similarly, antenna A2 isaligned with metamaterial tracks 55 b and 56 b, and, as such, isconfigured to transmit a mm-wave beam at those mutually coupled tracksand receive reflected signals therefrom.

As a result, different regions of metamaterial tracks can be arranged onthe carrier structures and provide a different measurements. Preferably,the different regions at which the metamaterial tracks on a same carrierstructure are attached are spaced in a way that the coupling between aninner rings and an outer ring is negligible compared to the couplingbetween the rings on the different carrier structures. For example,tracks 55 a and 56 a are strongly coupled by a field effect, whereastracks 55 a and 55 b are weakly coupled or not coupled by a fieldeffect. For this reason, tracks 55 a and 56 a may form a first coupledpair of tracks and tracks 55 b and 56 b may form a second coupled pairof tracks.

An antenna A1 or A2 is associated to each mutually coupled structure.Preferably the antennas A1 and A2 should have a directionalcharacteristic that focusses their transmission and reception on theassociated rings of the metamaterial structures. Thus, antenna A1 has adirectional characteristic associated with tracks 55 a and 56 a (i.e., afirst mutually coupled structure), and antenna A2 has a directionalcharacteristic associated with tracks 55 b and 56 b (i.e., a secondmutually coupled structure).

In case of identical patterns of elementary structures, the displacementof the elementary structures on both carrier structures will bedifferent due to the different radius (d1=r1*da; d2=r2*da).Consequently, the change of the mm-wave property is lower on the innertrack than on the outer track. In other words, a same angle shift of theshaft 54 causes a different change in the coupling of the two pairs ofcoupled tracks, resulting in two different signal modulations (i.e.,amplitude and/or phase) in the receive signals generated by thedifferent coupled pair of tracks.

The receiver circuit of transceiver 45 may then use a differentialmeasurement to discriminate the applied torque which is more robustagainst external factors such as the influence of distance changes. Forexample, the receiver circuit may use signals received from the twomutually coupled structures to perform a differential measurement of theapplied torque via a differential algorithm applied to the two signals.

FIG. 5C is a schematic view of a torque measurement system 502 accordingto one or more embodiments. The torque measurement system 502 is similarto the torque measurement system 500 depicted in FIG. 5A, with theexception that the torque measurement system 502 includes additionalmetamaterial tracks on each rotatable target object 51 and 52. Twometamaterial tracks 55 a and 55 c are attached to rotatable targetobject 51 and two metamaterial tracks 56 a and 56 c are attached torotatable target object 52. Thus, a single mutually coupled structure isformed by tracks 55 a and 56 a.

The two mm-wave metamaterial tracks 55 a and 55 c attached to rotatabletarget object 51 are concentric loops located at different distancesfrom the rotational axis 53. Similarly, the two mm-wave metamaterialtracks 56 a and 56 c attached to rotatable target object 52 areconcentric loops located at different distances from the rotational axis53. Furthermore, tracks 55 c and 56 c are located at different distancesfrom the rotational axis 53 such that mutual coupling therebetween isweak or zero.

This arrangement is similar to the torque measurement system 401depicted in FIG. 5B, except the additional tracks 55 c and 56 c are notmutually coupled to each other or to any other track as is the case withtracks 55 b and 56 b. Instead, tracks 55 c and 56 c are referencemetamaterial tracks for their respective target object (i.e., carrierstructure) 51 or 52, may be used to determine an absolute angularposition of its respective target object 51 or 52, or may be used tomeasure a rotational speed of its respective target object 51 or 52.

Tracks 55 c and 56 c may both have an array of structures that has atleast one property that changes in the rotation direction, as explainedabove in reference to FIGS. 3A-3G. For example, a pattern of track 55 cmay have a 360°/N periodic change, where N is an integer greater thanzero. Thus, track 55 c may be configured to modify an electro-magnetictransmit signal as it rotates, thereby producing an electro-magneticreceive signal having a periodic change proportional to a rotationalspeed of target object 51. The periodic change may be a periodic changein amplitude or phase induced by the rotation of track 55 c. As aresult, the rate of periodic change, akin to a frequency is proportionalto a rotational speed of track 55 c that can be measured by thetransceiver. A rate of change in measured angular values via track 55 ccould also be used to measure the rotational speed of track 55 c. Track56 c may be used in a similar manner for measuring the rotational speedof its target object 52. The rotational speeds of tracks 55 c and 56 care equal to the rotational speed of the shaft 54.

When N=1, the characteristic or property of the metamaterial at aspecific position along the track results an angle-dependent behavior orinteraction with an mm-wave, where the angle-dependent behavior orinteraction is an angle-dependent reflection, angle-dependentabsorption, angle-dependent transmission, or an angle-dependentcombination thereof. Since multiple of the metamaterial properties arechanging simultaneously, multiple mm-wave parameters of a signal eithertransmitted, reflected, or emitted by a metamaterial track will dependon the rotational angle. Two or more mm-wave parameters of a same signalor of different signals may be evaluated simultaneously to discriminatethe rotational position. Similarly, a single parameter of two or moresignals may also be evaluated to discriminate the rotational position.Consequently, a measurement of all relevant variations can be used toimprove the unambiguousness of the angle determination.

Here, three antennas A1, A2, and A3 are utilized, each having adirectional characteristic that focusses their transmission andreception on the one or more associated rings of the metamaterialstructures. Thus, antenna A1 has a directional characteristic associatedwith tracks 55 a and 56 a, antenna A2 has a directional characteristicassociated with track 55 c, and antenna A3 has a directionalcharacteristic associated with track 56 c

Thus, there is an additional metamaterial track 55 c, read by antennaA2, that is added on the front carrier structure 51 without a couplingtrack on the backside carrier structure 52, and an additionalmetamaterial track 56 c, read by antenna A3, that is added to thebackside carrier structure 52 without a coupling to the front sidecarrier structure 51. Consequently, the mm wave properties of thosereference tracks 55 c and 56 c are not influenced by the displacement ofthe two carrier structures relative to each other due to mutual couplingand are therefore torque independent. Whereas the mutual couplingbetween tracks 55 a and 56 a and the mutual coupling between tracks 55 band 56 b are torque dependent.

These reference tracks 55 c and 56 c can be used by the receiver circuitof the transceiver 45 as references for measurements that can be used toeliminate influences resulting from the setup, e.g., variations of thedistance between the antennas and the distance between the two carrierstructures 51 and 52.

For example, the receiver circuit of the transceiver 45 may beconfigured to determine a torque-independent absolute angular positionof the carrier structure 51 by analyzing an amplitude modulation or aphase modulation of a receive signal received from track 55 c at antennaA2 in reference to a carrier signal transmitted by the antenna A2 basedon methods described above. The receiver circuit may use thetorque-independent absolute angular position as the actual absoluteangular position of the carrier structure 51, which may be further usedto calculate the rotational speed thereof. Additionally, the receivercircuit may use the torque independent absolute angular position todetect preexisting errors in the set up and compensate the torquedependent measurements.

Similarly, the receiver circuit of the transceiver 45 may be configuredto determine a torque independent absolute angular position of thecarrier structure 52 by analyzing an amplitude modulation or phasemodulation of a receive signal received from track 56 c at antenna A3 inreference to a carrier signal transmitted by the antenna A3 based onmethods described above. The receiver circuit may use the torqueindependent absolute angular position as the actual absolute angularposition of the carrier structure 52, which may be further used tocalculate the rotational speed thereof. Additionally, the receivercircuit may use the torque independent absolute angular position todetect preexisting errors in the set up and compensate the torquedependent measurements.

In addition, the torque independent structures may also be angleindependent. For example, tracks 55 c and 56 c may have a homogeneouspattern, such as the one shown in FIG. 2A, with known behavior for themeasurement of the distance between the track and the antenna.

FIG. 6 is a block diagram that illustrates structure of one example of atransceiver according to one or more embodiments. The transceiver 45includes relevant transmission circuitry and receiver circuitry to theembodiments described herein. It will also be appreciated that relevanttransmission circuitry and receiver circuitry may be divided between thetransmitter 45 a and receiver 45 b according to implementation.

Frequency modulation may be used on the transmitter side to characterizethe transfer function of the transmission channel including themetamaterial over frequency. However, a continuous carrier wave with aconstant frequency may also be used.

On the measurement side (receiver side), it would still be magnitude(amplitude) and phase or I and Q, which would be the most sophisticatedand flexible solution. However, with respect to cost, a system with aconstant frequency carrier may be preferable. In this case, thefrequency is chosen to be in a defined region with respect to the polesand zeros where the phase or amplitude transfer function has amonotonous behavior with respect to the modified property of themetamaterial. Then a local measurement of phase shift or amplitudeattenuation is used.

Accordingly, at least one transmission antenna 601 (TX antenna) and atleast one receiver antenna 602 (RX antenna) are connected to an RF frontend 603 integrated into a chip, which the RF front end may contain allthose circuit components that are required for RF signal processing.These circuit components comprise for example a local oscillator (LO),RF power amplifiers, low noise amplifiers (LNA), directional couplers(for example rat-race couplers, circulators, etc.), and mixers fordownmixing (or down-converting) the RF signals into baseband or anintermediate frequency band (IF band). The RF front end 603 may—possiblytogether with further circuit components—be integrated into a chip,which is usually referred to as a monolithic microwave integratedcircuit (MMIC).

The example illustrated shows a bistatic (or pseudo-monostatic) radarsystem with separate RX and TX antennas. In the case of a monostaticradar system, a single antenna would be used both to emit and to receivethe electromagnetic (radar) signals. In this case, a directional coupler(for example a circulator) may be used to separate the RF signals to beemitted from the received RF signals (radar echo signals). Radar systemsin practice usually have a plurality of transmission and receptionchannels (TX/RX channels) with a plurality of TX and RX antennas, whichmakes it possible, inter alia, to measure the direction (DoA) from whichthe radar echoes are received. In such multiple-input multiple-output(MIMO) systems, the individual TX channels and RX channels in each caseusually have an identical or similar structure.

In the case of a frequency-modulated continuous-wave (FMCW) radarsystem, the RF signals emitted by the TX antenna 601 may be for examplein the range of approximately 10 GHz to 500 GHz. However, the frequencybands that are applied here depend on the structures to be used for thegeneration of the metamaterial target. As mentioned, the RF signalreceived by the RX antenna 603 comprises the radar echoes (chirp echosignals), that is to say those signal components that are backscatteredat one or at a plurality of radar targets. The received RF signal isdownmixed for example into baseband (or an IF band) and processedfurther in baseband by way of analog signal processing (see analogbaseband signal processing chain 604). The analog signal processingcircuitry 604 essentially comprises filtering and possibly amplifyingthe baseband signal. The baseband signal is finally digitized (seeanalog-to-digital converter 605) and processed further in the digitaldomain. The digital signal processing chain may be implemented at leastpartly in the form of software that is able to be executed on aprocessor, for example a microcontroller, a digital signal processor(DSP) 606, or another computer unit. The overall system is generallycontrolled by way of a system controller 607 that may likewise beimplemented at least partly in the form of software that is able to beexecuted on a processor, such as for example a microcontroller. The RFfront end 603 and the analog baseband signal processing chain 604(optionally also the analog-to-digital converter 605) may be integratedtogether in a single MMIC (that is to say an RF semiconductor chip). Asan alternative, the individual components may also be distributed over aplurality of integrated circuits. A single DSP may receive respectivedigital receive signals from each of the receive antennas forcalculating rotational parameters of the rotatable shaft, includingrotational speed, rotational direction, angle, torque, etc.

The DSP 606 is configured to perform the aforementioned phase analysis,amplitude analysis, and/or frequency analysis to determine a rotationalparameter (e.g., rotational speed, rotational direction, absoluteangular position, and/or torque) of the metamaterial track and/or therotatable shaft based on the determined amplitude modulation and/orphase modulation. The phase modulation of a received signal may be aphase shift of the received signal with respect to a phase of thetransmitted mm-wave (i.e., of the carrier signal). Similarly, theamplitude modulation of a received signal may be an amplitude shift ofthe received signal with respect to an amplitude of the transmittedmm-wave.

The DSP 606 may be configured to determine a phase shift and/or anamplitude shift of a received signal and translate the shift into arotational parameter either directly from a single receive signal or incombination with another receive signal (e.g., two phase shifted receivesignals are used to determine rotational direction). For example, theDSP 606 may refer to a look-up table provided in memory that storesangular positions or values relative to a specific amplitude modulationand/or phase modulation when the track has a 360° periodical pattern.

In addition, the DSP 606 may analyze a phase shift between two receivesignals for determining an absolute angular position as describedherein. The DSP 606 may also calculate the rotational speed by analyzingthe rate of change in the angular values. Additionally, by obtaining twomeasurement signals (e.g., two 90° phase shifted signals), a rotationdirection of the rotatable target object may also be determined by theDSP 606. In general, two receive signals can be used to achieve a 360°unambiguous measurement range. For a system measuring in a limited rangethe property of the metamaterial must not necessarily be changedaccording to a sine/cosine system. For a limited range (e.g., +/−60°), asine alone would be sufficient.

Metamaterial-based sensors with millimeter (mm)-wave radars as read-outhave the potential to overcome many challenges of existing sensorsystems. These mm-wave metamaterials represent a novel sensor concept inthe fields of torque, speed, and position measurements in bothrotational and linear movement sensors. Mm-wave metamaterials are fullytelemetric and highly scalable. Due to their high scalability, thisconcept allows the implementation of dual or multiple measurements inparallel without requiring additional installation space.

In order to maintain high robustness in harsh environment, dualmeasurement or differential measurement within the sensor may berequired. Furthermore, a combination of torque and speed measurement inone sensor provides a direct power flow sensor system.

One or more embodiments provide a method to implement multiple parallelmeasurements in metamaterial-based sensor systems. The idea is toimplement frequency multiplexing and therewith differentiate between thesignals in frequency space. The metamaterial structures are designedwith different working frequencies by varying their geometricalparameters. Read-out is done either using multiple radar chips withnon-overlapping bandwidth or using one radar chip performing frequencymodulation. The measuring and the read-out of various measurementparameters such as a rotational speed of the rotational shaft, anabsolute angular position of the rotational shaft, a rotation directionof the rotational shaft, and/or a torque applied to the rotational shaftcan be performed in parallel by using different arrays of mm-wavestructures (e.g., metamaterial tracks) for each measurement parameter.Each measurement parameter is assigned a different working frequencyaccording to its corresponding arrays of mm-wave structures. As aresult, an electro-magnetic signal with a frequency within the bandwidthof the target working resonance frequency can be used to measure acorresponding measurement parameter. Different electro-magnetic signalswith different frequencies within the bandwidth of their respectivetarget working resonance frequency can be used in parallel to measurethe different measurement parameters.

The electro-magnetic signals may be monochromatic or frequency modulated(e.g., a frequency ramp signal) with a correspondingly small bandwidththat only covers one of the target resonance frequencies. For example,In FIG. 7 , for example, one could use on frequency modulatedtransmitter with a bandwidth from 54 GHz to 60 GHz and a secondfrequency modulated transceiver with a bandwidth from 60 GHz to 66 GHz.In this case, a frequency modulated signal with ramps that change from54 GHz to 60 GHz, or vice versa, and a frequency modulated signal withramps that change from 60 GHz to 66 GHz, or vice versa, are generated.Each frequency modulated signal overlaps with a different targetresonance frequency and does not overlap with the other target resonancefrequency, as will be explained in further detail below.

The sensor effect of metamaterials is based on their characteristicresonance frequency. It is the tuning of this resonance frequency thattranslates the desired measurand into a tuning of reflected ortransmitted radar waves. The characteristic resonance of metamaterialsexhibits high Q-factors, also for single layered metamaterials. Thus, asingle metamaterial array signal has a narrow bandwidth. Adjustment ofthe metamaterial array to a shifted resonance frequency with the sameQ-factor is achievable. This working frequency is adjusted by varyingthe size of the elementary structures of the array or by varying thegeometric parameters within the elementary structures. The metamaterialsare then arranged in arrays comprising a multitude of elementarystructures. Further, the working frequency can be adjusted by varyingthe arrangement of elementary structures within the array.

The idea is to fabricate two or more metamaterial arrays with narrowbandwidths of their resonance frequency. The overlap between the twobandwidths is zero or negligible. An exemplary representation of thespectra from two resonances coming from two metamaterial arrays is shownin FIG. 7 . Specifically, FIG. 7 illustrates a resonance of a firstmetamaterial array and a resonance of a second metamaterial array, wherethe two metamaterial arrays have different working resonancefrequencies. A metamaterial array with a certain working resonancefrequency reacts strongly to signals that have a frequency within itsbandwidth and reacts weakly or not at all to signal having frequenciesoutside its bandwidth. Thus, each metamaterial array can be used for adifferent measurand along with an electro-magnetic signal whosefrequency targets the working resonance frequency of its targetmetamaterial array.

The metamaterial arrays can be spatially separated as separatemetamaterial tracks or nested (e.g., intermixed) within each other.Spatial separation is shown in FIG. 4A, for example. FIG. 8 shows anested arrangement of two metamaterial arrays, where a firstmetamaterial array includes a first type of elementary structures 81 andhas a first working resonance frequency and a second metamaterial arrayincludes a second type of elementary structures 82 and has a second,different working resonance frequency. Further, this principle can bescaled to a three or more metamaterial arrays, each having differentworking resonance frequencies. The metamaterial arrays may be arrangedon a same carrier structure, with the exception of torque—which requiresat least one metamaterial array to be arranged on a second carrierstructure.

Two metamaterial arrays used for torque measurements react as a mutuallycoupled structure with a common resonance frequency that results fromthe mutual coupling to generate a single measurement signal in responseto receiving an electro-magnetic signal within the bandwidth of theirworking resonance frequency. For example, metamaterial arrays 55 and 56and are mutually coupled to each other by a torque dependent coupling,thereby forming a mutually coupled structure with a common resonancefrequency that is sensitive to a torque dependent angular shift betweenmetamaterial array 55 and metamaterial array 56. Together, themetamaterial arrays 55 and 56 convert an electro-magnetic transmitsignal into an electro-magnetic receive signal based on a torque appliedto the rotational shaft that causes the torque dependent angular shift.In this way the torque can be measured using an electro-magnetictransmit signal whose frequency is within the bandwidth of the targetworking resonance frequency of the mutually coupled structure formed bymetamaterial arrays 55 and 56 (i.e., within the bandwidth of the commonresonance frequency).

Two metamaterial arrays used for measuring a rotation direction may havedifferent working resonance frequencies so that they can be measuredsimultaneously, in parallel. In other words, to separate measurementsignals are acquired, one from each of the metamaterial arrays. Thus,two electro-magnetic transmit signals are transmitted—one with afrequency within the bandwidth of the working resonance frequency of ametamaterial array 43 and one with a frequency within the bandwidth ofthe working resonance frequency of a metamaterial array 44, for example.In response, each metamaterial array generates its own measurementsignals (i.e., electro-magnetic receive signal) in response to receivingthe electro-magnetic transmit signal within its working resonancefrequency. These measurement signals from the two metamaterial arrayscan then be evaluated to detect their respective zero-crossings and aphase shift between the two measurement signals for determining therotation direction.

Thus, metamaterial arrays 43 and 44 may be configured with differentworking resonance frequencies in order to measure different rotationalparameters (e.g., rotation speed or absolute rotation angle) or tomeasure a same rotational parameter, such as rotation direction.Additional metamaterial arrays may be added to the carrier structure 40to measure additional rotational parameters with each additionalmetamaterial array having a different, non-overlapping working resonancefrequency with respect to the other working resonance frequencies.

Additionally, the mutually coupled structure formed by metamaterialarrays 55 a and 56 a is configured with a common working resonancefrequency to measure torque (e.g., a first torque measurement), themutually coupled structure formed by metamaterial arrays 55 b and 56 bis configured with a common working resonance frequency to measuretorque (e.g., a second torque measurement) but has a common workingresonance frequency that is different from the common working resonancefrequency of the mutually coupled structure formed by metamaterialarrays 55 a and 56 a so that measurements can be performed in parallel.Additionally, metamaterial arrays 55 c and 56 c are used to measureadditional measurands and thus have different working resonancefrequencies from each other and from metamaterial arrays 55 a, 56 a, 55b, and 56 b.

Read-out is done either with multiple transceivers (e.g., differentradar chips), each working in one of the metamaterial bandwidths, orwith one transceiver performing frequency modulation to transmitelectro-magnetic signals having different frequencies that targetdifferent working resonance frequencies in order to target differentmetamaterial arrays or measurands. Stepped frequency modulation is alsoapplicable.

FIGS. 9A-9F illustrate cross-sectional views of different possibletransceiver or transmitter/receiver implementations for differentarrangements of metamaterial arrays according to one or moreembodiments.

FIG. 9A illustrates a rotation sensor system 900A according to one ormore embodiments. The rotation sensor system 900A includes a rotationalshaft 42, a carrier structure and three metamaterial arrays 43, 44, and49 arranged as spatially separate metamaterial tracks. The rotationsensor system 900 a also includes a signal transceiver 45 that transmitselectro-magnetic transmit signals at different frequencies or frequencyranges via frequency multiplexing and receives the correspondingelectro-magnetic receive signals from a target metamaterial array 43,44, or 49. Alternatively, the transceiver 45 may be used solely as atransmitter and a receiver is provided to receive the correspondingelectro-magnetic receive signals. Because each electro-magnetic transmitsignal is partially transmitted and partially reflected by its targetmetamaterial array, thereby converting the electro-magnetic transmitsignal into an electro-magnetic receive signal, the transmitter andreceiver may be placed on the same side of the carrier structure 40 oron opposite sides of the carrier structure, as discussed above.

Metamaterial array 43 is configured with a first working resonancefrequency, metamaterial array 44 is configured with a second workingresonance frequency, and metamaterial array 49 is configured with athird working resonance frequency. Metamaterial array 43 may be used tomeasure an absolute angular position of the rotational shaft 42,metamaterial array 44 may be used to measure a rotation direction of therotational shaft 42, and metamaterial array 49 may be used to measure arotational speed of the rotational shaft 42 or to measure a distancebetween the carrier structure 40 and the transceiver 45 to use incompensating other measurement signals due to, for example, vibration.Of course, the target measurand for each metamaterial array can be anyof the parameters and can be configured in any combination or order.

The metamaterial array 43 is configured to convert a firstelectro-magnetic transmit signal having a frequency in the bandwidth ofits working resonance frequency into a first electro-magnetic receivesignal that the receiver (e.g., DSP 606) uses to measure a firstrotational parameter. Due to their different working resonancefrequencies, metamaterial arrays 44 and 49 respond weakly to the firstelectro-magnetic transmit signal or not at all in a way that any signalsgenerated by them in response to the first electro-magnetic transmitsignal are filtered out or ignored by the receiver (e.g., DSP 606).

The metamaterial array 44 is configured to convert a secondelectro-magnetic transmit signal having a frequency in the bandwidth ofits working resonance frequency into a second electro-magnetic receivesignal that the receiver (e.g., DSP 606) uses to measure a secondrotational parameter. Due to their different working resonancefrequencies, metamaterial arrays 43 and 49 respond weakly to the secondelectro-magnetic transmit signal or not at all in a way that any signalsgenerated by them in response to the second electro-magnetic transmitsignal are filtered out or ignored by the receiver (e.g., DSP 606).

The metamaterial array 49 is configured to convert a thirdelectro-magnetic transmit signal having a frequency in the bandwidth ofits working resonance frequency into a third electro-magnetic receivesignal that the receiver (e.g., DSP 606) uses to measure a thirdrotational parameter. Due to their different working resonancefrequencies, metamaterial arrays 43 and 44 respond weakly to the thirdelectro-magnetic transmit signal or not at all in a way that any signalsgenerated by them in response to the third electro-magnetic transmitsignal are filtered out or ignored by the receiver (e.g., DSP 606).

As a result, the transceiver 45 can perform frequency multiplexing totransmit electro-magnetic signals at the three metamaterial arrays 43,44, 49, where all three metamaterial arrays receive each of theelectro-magnetic signals but only one of the metamaterial arrays isconfigured to respond strongly to an electro-magnetic signal due to anoverlap of the electro-magnetic signal's frequency with the bandwidth ofthe working resonance frequency of the metamaterial array of interest.Here, different measurands are sequentially measured by the transceiver45 based on the frequency multiplexing scheme.

In some cases, the three metamaterial arrays 43, 44, 49 may receive anelectro-magnetic signal and produce their own respectiveelectro-magnetic receive signals therefrom. For example, theelectro-magnetic signal may be a frequency ramp signal that iscontinuously generated (e.g., as an FMCW signal) over a range offrequencies. The metamaterial arrays 43, 44, 49 strongly react to thefrequency ramp signal when the frequency of the ramp signal is withinthe bandwidth of its working resonance frequency, thereby producing astrong electro-magnetic receive signal that can be detected and measuredby the receiver. The receiver can filter out the weaker signals, forexample, that do not exceed a threshold.

FIG. 9B illustrates a rotation sensor system 900B according to one ormore embodiments. The rotation sensor system 900B is similar to therotation sensor system 900A, with the exception that the threemetamaterial arrays 43, 44, and 49 are nested within each other and areintermixed within a single metamaterial track 90 arranged around therotation shaft 42 on the carrier structure 40. The rotation sensorsystem 900B operates with a similar frequency multiplexing schemedescribed above in reference to the rotation sensor system 900A.

FIG. 9C illustrates a rotation sensor system 900C according to one ormore embodiments. The rotation sensor system 900C is similar to therotation sensor system 900A with the exception that multipletransceivers 45-1, 45-2, and 45-3 are used or multipletransmitter/receiver pairs are used with the receives 45 b-1, 45 b-2,and 45 b-3 arranged on the opposite side of the carrier structure 40than their transmitter counterparts.

Transceiver 45-1 is configured to target metamaterial array 44 withelectro-magnetic transmit signals. The transceiver 45-1 is configured totransmit electro-magnetic transmit signals having a frequency in thebandwidth of the working resonance frequency of metamaterial array 44 inorder to measure and process electro-magnetic receive signals therefrom.

Transceiver 45-2 is configured to target metamaterial array 43 withelectro-magnetic transmit signals. The transceiver 45-2 is configured totransmit electro-magnetic transmit signals having a frequency in thebandwidth of the working resonance frequency of metamaterial array 43 inorder to measure and process electro-magnetic receive signals therefrom.

Transceiver 45-3 is configured to target metamaterial array 49 withelectro-magnetic transmit signals. The transceiver 45-3 is configured totransmit electro-magnetic transmit signals having a frequency in thebandwidth of the working resonance frequency of metamaterial array 49 inorder to measure and process electro-magnetic receive signals therefrom.

The receivers are sensitive to or tuned to frequencies that are in thebandwidth of the working resonance frequency of their targetmetamaterial array.

This configuration enables measurements to be performed simultaneously,in parallel. Additionally, cross-talk between transmitted and receivedsignals is mitigated due to the electro-magnetic transmit signalstransmitted by the transceivers having different frequencies orfrequency ranges and due to the metamaterial arrays or mutually coupledstructures having different, non-overlapping or substantiallynon-overlapping working resonance frequencies.

FIG. 9D illustrates a rotation sensor system 900D according to one ormore embodiments. The rotation sensor system 900D is similar to therotation sensor system 900C, with the exception that the threemetamaterial arrays 43, 44, and 49 are nested within each other and areintermixed within a single metamaterial track 90 arranged around therotation shaft 42 on the carrier structure 40. The rotation sensorsystem 900D operates with a similar frequency multiplexing schemedescribed above in reference to the rotation sensor system 900C.

FIG. 9E illustrates a rotation sensor system 900E according to one ormore embodiments. The rotation sensor system 900E has two carrierstructures 51 and 52 in order to measure torque applied to rotationalshaft 54. Metamaterial arrays 55 a, 55 b, 55 c, and 56 c are arranged oncarrier structure 51 and are spatially separated into differentmetamaterial tracks. Each of the metamaterial arrays 55 a, 55 b, 55 c,and 56 c have different non-overlapping or substantially non-overlappingworking resonance frequencies. Metamaterial arrays 56 a and 56 b arearranged on carrier structure 52 and are spatially separated intodifferent metamaterial tracks. Metamaterial array 56 c could also bearranged on carrier structure 52 instead of on carrier structure 51.Each of the metamaterial arrays 56 a, 56 b, and 56 c have differentnon-overlapping or substantially non-overlapping working resonancefrequencies. However, metamaterial array 56 a a mutual working resonancefrequency with metamaterial array 55 a and metamaterial array 56 b has amutual working resonance frequency with metamaterial array 55 b. In thisway, metamaterial arrays 55 a and 56 a form a mutually coupled structureand metamaterial arrays 55 b and 56 b form another mutually coupledstructure, and both mutually coupled structures can be used to measuretorque.

Transceiver 45-1 is configured to mutually coupled metamaterial arrays55 a and 56 a and mutually coupled metamaterial arrays 55 b and 56 b byusing frequency multiplexing to serially transmit electro-magnetictransmit signals at different frequencies in order to target one of thetwo mutually coupled pairs. In particular, the transceiver 45-1 isconfigured to transmit electro-magnetic transmit signals having afrequency in the bandwidth of the working resonance frequencies ofmetamaterial arrays 55 a and 56 a in order to measure and processelectro-magnetic receive signals therefrom. Additionally, thetransceiver 45-1 is configured to transmit electro-magnetic transmitsignals having a frequency in the bandwidth of the working resonancefrequencies of metamaterial arrays 55 b and 56 b in order to measure andprocess electro-magnetic receive signals therefrom.

Transceiver 45-2 is configured to target metamaterial array 55 c withelectro-magnetic transmit signals. The transceiver 45-2 is configured totransmit electro-magnetic transmit signals having a frequency in thebandwidth of the working resonance frequency of metamaterial array 55 cin order to measure and process electro-magnetic receive signalstherefrom. This measurement can be performed in parallel with ameasurement that targets mutually coupled metamaterial arrays 55 a and56 a or mutually coupled metamaterial arrays 55 b and 56 b.

Transceiver 45-3 is configured to target metamaterial array 55 c withelectro-magnetic transmit signals. The transceiver 45-3 is configured totransmit electro-magnetic transmit signals having a frequency in thebandwidth of the working resonance frequency of metamaterial array 55 cin order to measure and process electro-magnetic receive signalstherefrom. This measurement can be performed in parallel with ameasurement that targets mutually coupled metamaterial arrays 55 a and56 a or mutually coupled metamaterial arrays 55 b and 56 b.

The receivers are sensitive to or tuned to frequencies that are in thebandwidth of the working resonance frequency of their targetmetamaterial array(s).

FIG. 9F illustrates a rotation sensor system 900F according to one ormore embodiments. The rotation sensor system 900F is similar to therotation sensor system 900E, with the exception that metamaterial arrays55 a and 55 b are nested within each other and are intermixed within asingle metamaterial track 91 arranged around the rotation shaft 54 onthe carrier structure 51, metamaterial arrays 56 a and 56 b are nestedwithin each other and are intermixed within a single metamaterial track92 arranged around the rotation shaft 54 on the carrier structure 52,and metamaterial arrays 55 c and 56 c are nested within each other andare intermixed within a single metamaterial track 93 arranged around therotation shaft 54 on the carrier structure 51.

Additionally, one or more transceivers is provided. Here, a singletransceiver 45 is provided that performs frequency multiplexing togenerate electro-magnetic transmit signals at different frequencies totarget different working resonance frequency bandwidths. In this way,different metamaterial arrays or different mutually coupled metamaterialarrays can be targeted for measurement without cross-talk.

In some cases, the metamaterial arrays may receive an electro-magneticsignal and produce their own respective electro-magnetic receive signalstherefrom. For example, the electro-magnetic signal may be a frequencyramp signal that is continuously generated (e.g., as an FMCW signal)over a range of frequencies. The metamaterial arrays strongly react tothe frequency ramp signal when the frequency of the ramp signal iswithin the bandwidth of its working resonance frequency, therebyproducing a strong electro-magnetic receive signal that can be detectedand measured by the receiver. The receiver can filter out the weakersignals, for example, that do not exceed a threshold.

Similar principles described above also apply to a linear positionsensor system. In particular, FIGS. 10A and 10B illustrate across-section view and a plan view, respectively, of a linear positionsensor system 1000 according to one or more embodiments. In this case, alinear movable target object 70 configured to move linearly in a linearmoving direction on a linear axis 71. Three mm-wave metamaterial arrays73-75 are arranged in spatially separated tracks that are coupled to thelinear movable target object 70 such that the mm-wave metamaterialtracks 73-75 each extend lengthwise along the linear moving direction.Alternatively, the metamaterial arrays 73-75 can be nested within eachother in a single metamaterial track. In either case, each of themetamaterial arrays 73-75 have different non-overlapping orsubstantially non-overlapping working resonance frequencies.

The mm-wave metamaterial array 73 is made up of a first array ofelementary structures having at least one first characteristic thatchanges along the mm-wave metamaterial array in the linear movingdirection, similar to the way the configuration of the array ofelementary structures changes around the perimeter of the mm-wavemetamaterial array in the previous examples related to rotationalposition sensing. The elementary structures of mm-wave metamaterialarray 73 may, for example, have an L/N periodical pattern where thecharacteristic change repeats N times over the length L of the mm-wavemetamaterial array. N may be an integer equal to or greater than one.The length L of the mm-wave metamaterial array 73 may also equal thelength of the linear movable target object 70 or a range of linearmotion that the linear movable target object 70 undergoes. The mm-wavemetamaterial array 73 generates a receive signal A (e.g., a reflectionsignal) when an mm-wave beam is incident thereon at the illuminatedsegment 73 i of the array and has a frequency within the bandwidth ofthe working resonance frequency of metamaterial array 73. Themetamaterial array 73 may be used to measure a linear speed, a movementdirection, or an absolute linear position of the linear movable targetobject 70.

The mm-wave metamaterial array 74 is made up of a second array ofelementary structures having at least one second characteristic thatchanges along the mm-wave metamaterial array in the linear movingdirection, similar to the way the configuration of the array ofelementary structures changes around the perimeter of the mm-wavemetamaterial array in the previous examples related to rotationalposition sensing. The elementary structures of mm-wave metamaterialarray 74 may, for example, have an L/N periodical pattern where thecharacteristic change repeats N times over the length L of the mm-wavemetamaterial array. N may be an integer equal to or greater than one.The mm-wave metamaterial array 74 generates a receive signal B (e.g., areflection signal) when an mm-wave beam is incident thereon at theilluminated segment 74 i of the array and has a frequency within thebandwidth of the working resonance frequency of metamaterial array 74.The periodical patten of mm-wave metamaterial array 74 may be linearlyshifted in the linear moving direction relative to the periodical pattenof mm-wave metamaterial array 73 such that receive signal B is shifted90° with respect to receive signal A. The metamaterial array 74 may beused to measure a different measurand from metamaterial array 73,including a linear speed or an absolute linear position of the linearmovable target object 70 or may be used in conjunction with metamaterialarray 73 to measure specific measurand, including a movement directionof the linear movable target object 70.

The mm-wave metamaterial array 75 is made up of a third array ofelementary structures having at least one third characteristic thatchanges along the mm-wave metamaterial array in the linear movingdirection, similar to the way the configuration of the array ofelementary structures changes around the perimeter of the mm-wavemetamaterial array in the previous examples related to rotationalposition sensing. The elementary structures of mm-wave metamaterialarray 75 may, for example, have a single periodical pattern that extendsthe length L of the mm-wave metamaterial array such that thereflectivity and/or transmittivity of the array is unique for eachdiscrete linear position. Thus, the configuration of the array ofelementary structures is unique to a linear position of the mm-wavemetamaterial array on the linear movable target object 70.

The mm-wave metamaterial array 75 generates a receive signal R (e.g., areflection signal) when an mm-wave beam is incident thereon at theilluminated segment 75 i of the array and has a frequency within thebandwidth of the working resonance frequency of metamaterial array 75.Because only a signal period of characteristic change is encoded ontoarray 75, the phase shift and/or amplitude shift of the receive signal Ris unique to the absolute linear position of the linear movable targetobject 70.

Alternatively, the third array of elementary structures of themetamaterial array 75 may have a configuration that does not changealong the length of the mm-wave metamaterial array, similar to the arrayshown in FIG. 2A and may be used to measure a distance between the arrayand the transceiver in order to compensate the other measurement signalsfor vibration.

The linear position sensor system 1000 further includes at least one ofa transceiver, transmitter, and/or receiver combination. For example,the linear position sensor system 1000 may include a transceiver 45having a transmitter antenna 601 configured to transmit mm-waves (i.e.,electro-magnetic transmit signals) at the metamaterial arrays 73-75 atdifferent frequencies. The transceiver 45 also includes a receiverantenna 602 configured to receive a partially-reflected mm-waves (i.e.,electro-magnetic receive signals A, B, and R) from the metamaterialarrays 73-75.

Alternatively, the linear position sensor system 1000 may includereceiver 45 b that includes receiver antenna 608 that is configured toreceive a partially transmitted mm-waves (i.e., electro-magnetic receivesignals A, B, and R) as a result of the transmitted mm-waves interactingwith (i.e., being partially absorbed by and transmitted through) themetamaterial arrays 73-75. Additional transceivers, transmitters, and/orreceivers can be used for transmitting to and receiving from targetsmetamaterial arrays 73-75 in a similar manner discussed above inreference to FIGS. 9A-9F, and serial and/or parallel measurements arepossible depending on the transceiver/transmitter/receiver configurationused.

The receiver circuitry (e.g., DSP 606) either at transceiver 45 or atreceiver 45 b is configured to receive the electro-magnetic receivesignals A, B, and R and determine a linear speed, movement direction,and/or absolute linear position of the linear movable target object 70based on the received electro-magnetic signals A, B, and/or R.

For example, the mm-wave metamaterial array 73 may be configured tomodify an electro-magnetic transmit signal, thereby producing theelectro-magnetic receive signal A having a property unique to the linearposition of the mm-wave metamaterial array at which the electro-magnetictransmit signal is incident, and at least one processor is configured toevaluate the property of the received electro-magnetic receive signal A,and determine the linear speed of the linear movable target object basedon the evaluated property. The at least one processor is furtherconfigured to receive the electro-magnetic receive signal B anddetermine a linear movement direction of the linear movable targetobject 70 based on the received electro-magnetic signals A and B and,more particularly, based on the positive or negative phase shiftthereof. The at least one processor is further configured to receive theelectro-magnetic receive signal R and determine an absolute linearposition of the linear movable target object 70 based on the receivedelectro-magnetic signal R according to a unique phase shift and/oramplitude shift that corresponds to the linear position of the linearmovable target object 70.

In some cases, the metamaterial arrays 73-75 may receive anelectro-magnetic signal and produce their own respectiveelectro-magnetic receive signals therefrom. For example, theelectro-magnetic signal may be a frequency ramp signal that iscontinuously generated (e.g., as an FMCW signal) over a range offrequencies. The metamaterial arrays strongly react to the frequencyramp signal when the frequency of the ramp signal is within thebandwidth of its working resonance frequency, thereby producing a strongelectro-magnetic receive signal that can be detected and measured by thereceiver. The receiver can filter out the weaker signals, for example,that do not exceed a threshold.

In addition, torque sensors for powertrain components are in greatdemand as they would provide monitoring of true power transfer and thusopen up new possibilities for efficiency enhancement and safetyimprovement. Metamaterial-based mm-wave torque sensors have thepotential to meet the requirements within powertrains, such as limitedspace, telemetric read-out and robustness in harsh environment (e.g.,abrasion, dust, oil, fumes, electromagnetic interferences). One or moreembodiments provides a robust, low power and low-cost system formetamaterial-based mm-wave torque measurement, static or dynamic, usinga quadrature continuous-wave (QCW) mm-wave (e.g., radar) transceiver. Itis scalable over a broad range of working frequencies, from a few GHz toseveral hundred GHz. The QCW based sensor can be further applied toother rotational and linear movement sensors to measure variousrotational parameters or linear movement parameters that are robustagainst vibrations and other interferences that may cause the variationsin distance between the transceiver and the target object that need tobe accounted for to acquire accurate measurements.

FIG. 11 illustrates a schematic block diagram of a QWC radar transceiver1100 according to one or more embodiments. The QWC radar transceiver1100 is one type of transceiver that may be used as transceiver 45 inany of the above-described embodiments. The benefits of using a QWCradar transceiver will be described below.

The QCW radar transceiver 1100 is a direct down conversion transceiverwhere the received signal is divided into in-phase and quadrature (IQ)demodulated signals. The direct down conversion allows measurements ofphase or amplitude shifts caused by a target object (e.g., one or moremm-wave metamaterial arrays) with simple and low-cost radar components.Additionally, a QCW radar transceiver may overcome what is referred toas a “null point” issue. A null point issue occurs when the absolutedistance to the target object causes a phase shift equal to an oddmultiple of π/2. The null point occurs if the distance between antennaand metamaterial is close to an uneven multiple of half the wavelengthof the mm-waves. This issue is completely avoided using I/Q demodulationof the received signal, as described herein.

Similar to that described above with respect to transceiver 45, the QCWradar transceiver 1100 is used to measure the change in reflection ortransmission of the received signal relative to the transmitted signal(e.g., a phase shift or an amplitude shift), which is caused by arotational parameter of a rotational shaft (e.g., shaft 42 or 54). Therotational parameter may be rotational angle, rotational speed,rotational direction, or rotational torque. In principle, the overallQCW radar transceiver 1100 can act as an envelope detector or amplitudemodulation (AM) detector, whereby the modulation comes from theinteraction of the transmit signal with the metamaterial. For example,the QCW radar transceiver 1100 includes a transmitter antenna 601configured to transmit a continuous wave towards at least onemetamaterial track, and the at least one metamaterial track isconfigured to convert the continuous wave into a receive signal based ona rotational parameter of the rotational shaft. The QCW radartransceiver 1100 further includes a receiver antenna 602 that isconfigured to receive the receive signal. Through I/Q demodulation, theQCW radar transceiver 1100 is configured to acquire a measurement ofboth phase and amplitude of the receive signal, and determine ameasurement value for the rotational parameter of the rotational shaftbased on the measurement (e.g., based on the phase shift or amplitudeshift relative to the transmitted continuous wave).

The RF front end of the QCW radar transceiver 1100 comprises a localoscillator 1101 (LO) that generates an RF oscillator signal SLo. The RFoscillator signal SLo is also referred to as LO signal. In radarapplications, the LO signal is usually in the super high frequency (SHF)or extremely high frequency (EHF) band, e.g., in the range from 76 GHzto 81 GHz. A fair number of radar systems also operate in the 24 GHz ISMband (industrial, scientific and medical band). The LO signal SLo isprocessed both in the transmission signal path (in the TX channel) andin the received signal path (in the RX channel).

The transmission signal SRF transmitted by the TX antenna 601 isgenerated by amplifying the LO signal SLO, for example by means of theRF power amplifier, and is therefore merely an amplified and possiblyphase-shifted version of the LO signal SLO. The output of the amplifiercan be coupled to the TX antenna 601 (in the case of abistatic/pseudo-monostatic radar configuration). The received signal YRFreceived by the RX antenna 602 is supplied to the receiver circuit inthe RX channel and hence to the RF ports of an IQ mixer that includestwo mixers 1106 and 1107. In the present example, the RF received signalYRF (antenna signal) is pre-amplified by means of the amplifier 1103(gain g). The mixers 1106 and 1107 thus receive the amplified RFreceived signal gYRF. The amplifier 1103 can be, for example, alow-noise amplifier (LNA).

The mixers 1106 and 1107 receive the amplified RF received signal gYRFfrom a power splitter 1104 that is configured to split the amplified RFreceived signal gYRF into two equivalent signals YRF1 and YRF2 withequal power. In this example, the power splitter 1104 may be a zerodegree power splitter. Both signals YRF1 and YRF2 are representative ofgYRF, but with divided power.

The reference port of each mixer 1106 and 1107 is supplied with the LOsignal SLO via two power splitters 1102 and 1105, so that the mixers1106 and 1107 down-converts their respective RF received signals YRF1and YRF2 to baseband. The power splitter 1102 may be a zero degree powersplitter that splits that LO signal SLO into two equivalent signals: oneLO signal SLO1 for generating the transmission signal SRF (SLO1) and theother LO signal SLO2 used for IQ demodulation at the receiver channel.Both signals SLO1 and SLO2 are representative of SLO, but with dividedpower. The power splitter 1105 may be a 90 degree power splitter thatsplits that LO signal SLO into two equivalent signals, SLO2′ and SLO2″,that are 90° phase shifted from each other. For example, power splitter1105 may generate SLO2′ to be used by mixer 1106 to demodulate signalYRF1 into a baseband signal SBBI (i.e., an in-phase demodulated signalor, simply, an I signal) and power splitter 1105 may generate SLO2″ tobe used by mixer 1107 to demodulate signal YRF2 into a baseband signalSBBQ (i.e., a quadrature demodulated signal or, simply, a Q signal). Theconversion in baseband can take place in one stage (that is to say fromthe RF band directly to baseband) or via one or more intermediate stages(that is to say from the RF band to an intermediate-frequency band andon to baseband). Accordingly, the mixer stage contains an IQ mixer thatgenerates two baseband signals (in-phase and quadrature signals) thatcan be interpreted as a real part and an imaginary part of a complexbaseband signal.

Both baseband signals SBBI and SBBQ may be passed through respectivelow-pass filters (LPFs) 1108 and 1109 to remove any unwanted signalcomponents therefrom, such as undesirable sidebands and imagefrequencies, so that the in-phase signal I is a DC value of basebandsignal SBBI and the quadrature signal Q is a DC value of the basebandsignal SBBQ. The in-phase signal I and the quadrature signal Q are thenprovided to the DSP 606, which uses both signals to perform ameasurement on a rotational parameter of the shaft. For example, the DSP606 may calculate the phase or the amplitude or both of RF receivedsignal YRF via digital samples of the I and Q signals acquired by ADC605.

The ability to adjust the distance between the transceiver 1100 and themetamaterial with high precision would enable the received basebandsignals to be at an optimum working point. The optimal working pointmeans that a small variation of the argument of the cosine causes alarge variation of the overall cosine function. However, when it is notpossible to adjust the distance between transceiver and metamaterialwith high precision, one cannot ensure to operate in the optimal workingpoint. This is overcome by implementing I/Q demodulation and using boththe I and the Q demodulated signals for the measurement. To obtain thephase angle, containing the phase modulation caused by the metamaterial,a possible I/Q demodulation method is to implement arctan demodulation.The phase angle ϕ can be ascertained using the arc-tangent function(also referred to as arctan, a tan or tan⁻¹), in accordance withEquation 1:

$\begin{matrix}{{\phi = {{\tan^{- 1}\frac{I}{Q}} = {\theta_{MM} + \frac{4\pi d}{\lambda}}}},} & {{Eq}.1}\end{matrix}$

where θ_(MM) is the phase modulation caused by the metamaterial and d isthe distance between the transceiver 1100 and the targeted metamaterialtrack. In other words, θ_(MM) is the phase shift of the receive signalYRF relative to the transmit signal SRF after the transmit signal SRFinteracts with the metamaterial. The term 4πd/λ is the phase shift dueto path length d between the transceiver 1100 and the receiver antenna602 (including the metamaterial arranged along the path).

The absolute amplitude A, containing the amplitude modulation caused bythe metamaterial, is calculated in accordance with Equation 2:

A=√{square root over (I ² +Q ²)}  Eq. 2.

To apply Equations 1 and 2, both the I and Q signals first have to benormalized. It is of course possible to evaluate both the absoluteamplitude and the phase angle to obtain the complete complex basebandsignal. This provides information from the metamaterial modulation ofboth the amplitude and phase modulation of the received signal. It ispossible to exploit this information to make the sensor more robust atthe cost of additional signal processing.

Shocks or vibrations lead to small changes or variations in distancebetween the transceiver 1100 to the target metamaterial track(s). DCoffset compensation and I/Q amplitude mismatch compensation may beperformed on signals I and Q prior to providing them to the ADC 605. Thebaseband signals in a QCW radar after DC offset compensation can bewritten according to Equations 3 and 4:

$\begin{matrix}{{I = {A_{{MM},I}\cos\left( {\theta_{MM} + \frac{4\pi d}{\lambda}} \right)}},} & {{Eq}.3}\end{matrix}$ $\begin{matrix}{{Q = {A_{{MM},Q}\sin\left( {\theta_{MM} + \frac{4\pi d}{\lambda}} \right)}},} & {{Eq}.4}\end{matrix}$

where A_(MM,I) is the amplitude of the in-phase signal I and A_(MM,Q) isthe amplitude of the quadrature signal Q. As can be appreciated, adependency on distance d is present. The modulation caused by smallvariations of distance d (between transceiver/radar and metamaterial) isalways superimposed with the modulation caused by the metamaterial.Thus, small variations in distance should be compensated. Thiscompensation, performed by the DSP 606, can be done by implementing areference measurement or a dual measurement. There are at least twopossibilities for implementing the dual measurement. For them frequencymultiplexing is applicable: (a) two-tone or dual tone QCW radar, and (b)a second QCW radar together with a second metamaterial array or areference trace.

For a reference measurement, the transceiver 1100 is configured totransmit a first transmit signal SRF with a set frequency while thetarget metamaterial track(s) has/have a known rotational parameter(e.g., a known speed, direction, angle, or applied torque) and recordthe phase angle and/or absolute amplitude measurement per Equations 1and 2 as reference values. For example, the metamaterial may be in azero position as a reference position (e.g., zero speed, zero angle,zero torque). When performing a measurement on the rotational parameter,the transceiver 1100 is configured to transmit a second transmit signalSRF with the same frequency as the first transmit signal, obtain the Iand Q signals, and, using the DSP 606, obtain the phase angle and/or theabsolute amplitude measurement, calculate a difference between themeasured value the corresponding reference value (i.e., the differencebetween the measured phase value and the reference phase value or thedifference between the measured absolute amplitude and the referenceabsolute amplitude value), and determine a measurement value of therotational parameter based on the measured difference. The, the DSP 606determines the measurement value for the rotational parameter based onthe measurement relative to the reference measurement.

As an example, the metamaterial track 43 is configured to generate areceive signal by changing a wave modulation property of a continuouswave based on a real-time value of the rotational parameter to bemeasured. The change of the wave modulation property is induced by achange in at least one of capacitive near field coupling, inductive nearfield coupling, waveguide coupling, or far field coupling correspondingto the real-time value of the rotational parameter. As a result, themetamaterial track 43 is configured to modify the continuous wave basedon a real-time value of the rotational parameter to be measured as themeasurement value, thereby producing the receive signal having ameasured difference to the reference measurement that is unique to thereal-time value of the rotational parameter.

To perform a more robust measurement against distance variations,two-tone or dual tone QCW radar may be used. The reference measurementis repeated using two different frequencies to obtain two referencevalues that are linked to their respective frequencies. This isimplemented by measuring at two different frequencies on onemetamaterial array, as illustrated in FIG. 12 . FIG. 12 illustrates anexample transmission spectra from a metamaterial array (e.g., track 43or 44) or a mutually coupled pair of metamaterial arrays (e.g., tracks55 and 56) over a frequency range. In other words, the transmissionspectra is that of receive signals that have interacted withmetamaterial. A reference signal is measured with a known rotationalquantity being present (e.g., known rotational angle or torque) and ameasurement signal is measured with an unknown rotational quantity to bedetermined by the transceiver 1100. In this example, measurement valuesare acquired at two different transmission frequencies f1 and f2 foramplitude measurement. Similar principles can be extended to a phasemeasurement.

Each transmitted signal SRF is a monochromatic continuous wave having afixed frequency. Moreover, each metamaterial track or each mutuallycouple pair of metamaterial tracks has a resonance bandwidth. The firstfrequency f1 is outside the resonance bandwidth and the second frequencyf2 is within the resonance bandwidth. As a result, signals transmittedwith the first frequency f1 will experience a small influence from themetamaterial (i.e., a small phase or amplitude shift) and signalstransmitted with the second frequency f2 will experience a largeinfluence from the metamaterial (i.e., a large phase or amplitudeshift). Accordingly, relative changes (X) and (Y) in the transmissionspectra are different at frequencies f1 and f2 for a particular value ofa rotational parameter. For example, for a particular rotational angleor a particular torque, difference values X and Y will be different.

To take a step back, the transceiver 1100 is configured to transmit afirst transmit signal SRF with frequency f1 while the targetmetamaterial track(s) has/have a known rotational parameter (e.g., aknown speed, direction, angle, or applied torque) and record the phaseangle and/or absolute amplitude measurement per Equations 1 and 2 asfirst reference values. The transceiver 1100 is also configured totransmit a second transmit signal SRF with frequency f2 while the targetmetamaterial track(s) has/have a known rotational parameter (e.g., aknown speed, direction, angle, or applied torque) and record the phaseangle and/or absolute amplitude measurement per Equations 1 and 2 assecond reference values. In this way, the DSP 606 obtains referencevalues at both frequencies f1 and f2. It will be appreciated that whiletwo separate transmit signals with two different frequencies may be usedvia frequency multiplexing to acquire two sets of reference values, atwo-tone signal or dual frequency signal could also be used to performthe measurements.

When performing a measurement on the rotational parameter, thetransceiver 1100 is configured to transmit a third transmit signal SRFwith frequency f1, obtain the I and Q signals, and, using the DSP 606,obtain the phase angle and/or the absolute amplitude measurement,calculate a first difference X between the measured value thecorresponding reference value (i.e., the difference between the measuredphase value and the reference phase value for frequency f1 or thedifference between the measured absolute amplitude and the referenceabsolute amplitude value for frequency f1).

The transceiver 1100 is further configured to transmit a fourth transmitsignal SRF with frequency f2, obtain the I and Q signals, and, using theDSP 606, obtain the phase angle and/or the absolute amplitudemeasurement, calculate a second difference Y between the measured valuethe corresponding reference value (i.e., the difference between themeasured phase value and the reference phase value for frequency f2 orthe difference between the measured absolute amplitude and the referenceabsolute amplitude value for frequency f2).

It will be appreciated that while two separate transmit signals with twodifferent frequencies may be used to via frequency multiplexing toacquire two sets of measurement values, a two-tone signal or dualfrequency signal could also be used to perform the measurements.

The DSP 606 is configured to calculate the phase angle and/or theabsolute amplitude of the receive signal YRF based on the firstdifference and the second difference. Due to one frequency being withinthe resonance bandwidth of the metamaterial and one frequency beingoutside the resonance bandwidth, the relative changes in thetransmission spectra are different at frequencies f1 and f2. The twodifference values X and Y, in combination, are unique to a value of themeasured rotational parameter. Thus, the DSP 606 may use, for example, alookup table that references difference values X and Y to determine ameasurement value of the rotational parameter. This dual referencemeasurement cancels out phase shifts from distance variations betweenthe antenna and the metamaterial. Further, it compensates for pathlosses between the antennas and the metamaterial (e.g., dust, abrasions,humidity, etc.) as long as the reflected or transmitted waves are stilldetectable.

Regarding using a second QCW radar together with a second metamaterialarray, two metamaterial arrays are designed such that a change inreflection or transmission is different between them. In other words,two metamaterial arrays may have different resonance bandwidths. Forexample, metamaterial tracks 43, 44, and 49 may have different resonancebandwidths, or reference track 55 c or 56 c may be implemented with adifferent resonance bandwidth, or mutually coupled pairs 55 a/56 c and55 b/56 b may have different resonance bandwidths. The difference inmodulation produced by tracks having different resonance bandwidths canbe used to calculate the rotational parameter.

In this case, the transceiver 1101 may transmit a first transmissionsignal at, for example, frequency f1 that is inside the resonancebandwidth of a first metamaterial track and outside the resonancebandwidth of the second metamaterial track, and obtain the phase and/oramplitude measurement from each metamaterial track using the firsttransmission signal. The transceiver 1101 may the transmit a secondtransmission signal at, for example, frequency f2 that is inside theresonance bandwidth of the second metamaterial track and outside theresonance bandwidth of the first metamaterial track, and obtain thephase and/or amplitude measurement from each metamaterial track usingthe first transmission signal.

For a phase measurement, the DSP 606 is then configured to calculate afirst phase difference between the phase measurements resultant from thefirst transmission signal transmitted at frequency f1, calculate asecond phase difference between the phase measurements resultant fromthe second transmission signal transmitted at frequency f2, anddetermine the measurement value of the rotational parameter based on thefirst and the second differences. Read-out is done with two transceiversoperating at different transmission frequencies or one transceivervarying between two frequencies. Time-multiplexing is also applicable.

For absolute amplitude measurement, the DSP 606 is then configured tocalculate a first amplitude difference between the absolute amplitudemeasurements resultant from the first transmission signal transmitted atfrequency f1, calculate a second amplitude difference between theabsolute amplitude measurements resultant from the second transmissionsignal transmitted at frequency f2, and determine the measurement valueof the rotational parameter based on the first and the seconddifferences (e.g., by using a lookup table). Read-out is done with twotransceivers operating at different transmission frequencies or onetransceiver varying between two frequencies. Time-multiplexing is alsoapplicable.

Regarding using a reference track, two tracks may be used with one beingmade of metamaterial and one being made without metamaterial (e.g., abare metal track). This bare reference track may be used as a substituteto a track previously disclosed herein (e.g., track 43, 44, 49, 55 c, or56 c). As a result of being void of metamaterial, the phase or amplitudemodulation shift produced by the reference track is merely a function ofpath length d. Accordingly, the transceiver 1101 can transmit a firstcontinuous wave at the metamaterial track that produces a receive signalfrom the first continuous wave transmit signal. The transceiver 1101 isconfigured to receive the receive signal and the DSP 606 is configuredto acquire a measurement of the phase angle or absolute angle via I/Qmodulation as a first measurement. Furthermore, the transceiver 1101 cantransmit a second continuous wave at the reference track that produces areference signal from the second continuous wave transmit signal. Thetransceiver 1101 is configured to receive the reference signal and theDSP 606 is configured to acquire a measurement of the phase angle orabsolute angle of the reference signal via I/Q modulation and measure apath length d (substantially the same distance to the metamaterialtrack) based on the measurement. The DSP 606 can then use the distancemeasurement to perform compensation on the first measurement acquiredfrom the targeted metamaterial to account to distance variations due tovibration or shock.

Additionally, or alternatively, the transceiver 1101 is configured togenerate from the reference signal an in-phase demodulated signal and aquadrature demodulated signal, use the in-phase demodulated signal andthe quadrature demodulated signal to derive a second measurement of thephase or absolute amplitude, and determine the measurement value for therotational parameter based on the first and the second measurements. Forexample, a difference between the first and second measurements may becalculated by the DSP 606 and then used to determine the measurementvalue of the rotational parameter (e.g., via a lookup table).

Signal differentiation can be done in various ways. In the frequencyspace, different working frequencies of the metamaterial arrays arepossible. Read-out is then done with two transceivers or one transceivervarying between two frequencies. Time-multiplexing is also applicable.It is also possible to differentiate between the signals by measuring atdifferent positions of the disc and thereby avoid crosstalk between thereceivers.

Additional embodiments are provided below.

1. A sensor system, comprising: a first metamaterial track mechanicallycoupled to a rotational shaft configured to rotate about a rotationalaxis, wherein the first metamaterial track is arranged at leastpartially around the rotational axis, and wherein the first metamaterialtrack comprises a first array of elementary structures; at least onetransmitter configured to transmit a first continuous wave towards thefirst metamaterial track, wherein the first metamaterial track isconfigured to convert the first continuous wave into a first receivesignal based on a rotational parameter of the rotational shaft; and atleast one quadrature continuous-wave receiver configured to receive thefirst receive signal, acquire a first measurement of a first property ofthe first receive signal, and determine a measurement value for therotational parameter of the rotational shaft based on the firstmeasurement.

2. The sensor system of embodiment 1, further comprising: a secondmetamaterial track mechanically coupled to the rotational axis, whereinthe second metamaterial track is arranged at least partially around ofthe rotational axis, and wherein the second metamaterial track comprisesa second array of elementary structures, wherein the at least one istransmitter configured to transmit the first continuous wave towards thesecond metamaterial track, wherein the first and the second metamaterialtracks are configured, together, to convert the first continuous waveinto the first receive signal based on the rotational parameter of therotational shaft; and the at least one quadrature continuous-wavereceiver is configured to receive the first receive signal, acquire thefirst measurement of the first property of the first receive signal, anddetermine the measurement value for the rotational parameter of therotational shaft based on the first measurement.

3. The sensor system of embodiment 1, wherein: the at least onequadrature continuous-wave receiver is configured to evaluate the firstmeasurement relative to a first reference measurement that correspondsto the rotational parameter, and determine the measurement value for therotational parameter based on the first measurement relative to thefirst reference measurement.

4. The sensor system of embodiment 1, wherein the at least onequadrature continuous-wave receiver includes at least one processorconfigured to evaluate the first property using at least one of phaseanalysis, amplitude analysis, or spectral analysis, and determine themeasurement value for the rotational parameter based on the evaluatedfirst property.

5. The sensor system of embodiment 1, wherein the at least onequadrature continuous-wave receiver is configured to generate from thefirst receive signal a first in-phase demodulated signal and a firstquadrature demodulated signal, use the first in-phase demodulated signaland the first quadrature demodulated signal to derive the firstmeasurement, and determine the measurement value for the rotationalparameter based on the first measurement.

6. The sensor system of embodiment 5, wherein the first property is anamplitude of the first receive signal and the at least one quadraturecontinuous-wave receiver is configured to calculate the firstmeasurement of the first property of the first receive signal accordingto: Equation 2, wherein A denotes the first measurement, I denotes a DCvalue of the first in-phase demodulated signal, Q denotes a DC value ofthe first quadrature demodulated signal, and sqrt denotes a square rootfunction.

7. The sensor system of embodiment 5, wherein the first property is aphase of the first receive signal and the at least one quadraturecontinuous-wave receiver is configured to calculate the firstmeasurement of the first property of the first receive signal accordingto Equation 1, wherein 4 denotes the first measurement, I denotes a DCvalue of the first in-phase demodulated signal, and Q denotes a DC valueof the first quadrature demodulated signal.

8. The sensor system of embodiment 5, wherein the at least onequadrature continuous-wave receiver is configured to evaluate the firstmeasurement relative to a first reference measurement that correspondsto the rotational parameter and determine the measurement value of therotational parameter based on the first measurement relative to thefirst reference measurement.

9. The sensor system of embodiment 5, wherein the at least onequadrature continuous-wave receiver is configured to calculate adifference between the first measurement and the first referencemeasurement, and determine measurement value of the rotational parameterof the rotational shaft based on the difference.

10. The sensor system of embodiment 8, wherein the first referencemeasurement is a reference amplitude or a reference phase thatcorrespond to a reference value of the rotational parameter.

11. The sensor system of embodiment 1, wherein: the at least onetransmitter is configured to transmit a second continuous wave towardsthe first metamaterial track, wherein the first continuous wave is amonochromatic wave having a first frequency and the second continuouswave is a monochromatic wave having a second frequency different fromthe first frequency, the first metamaterial track is configured toconvert the second continuous wave into a second receive signal based onthe rotational parameter of the rotational shaft, and the at least onequadrature continuous-wave receiver is configured to receive the secondreceive signal, acquire a second measurement of the second receivesignal, and determine the rotational parameter based on the firstmeasurement and the second measurement.

12. The sensor system of embodiment 11, wherein: the at least onequadrature continuous-wave receiver is configured to evaluate the firstmeasurement relative to a first reference measurement acquired at thefirst frequency and that corresponds to the rotational parameter,evaluate the second measurement relative to a second referencemeasurement acquired at the second frequency and that corresponds to therotational parameter, and the at least one quadrature continuous-wavereceiver is configured to determine a first difference between the firstmeasurement and the first reference measurement, determine a seconddifference between the second measurement and the second referencemeasurement, and determine measurement value of the rotational parameterof the rotational shaft based on the first difference and the seconddifference.

13. The sensor system of embodiment 11, wherein the first metamaterialtrack has a resonance bandwidth, and the first frequency is within theresonance bandwidth and the second frequency is outside the resonancebandwidth.

14. The sensor system of embodiment 1, wherein the first metamaterialtrack is configured to generate the first receive signal by changing awave modulation property of the first continuous wave based on areal-time value of the rotational parameter to be measured, wherein thechange of the wave modulation property is induced by a change in atleast one of capacitive near field coupling, inductive near fieldcoupling, waveguide coupling, or far field coupling corresponding to thereal-time value of the rotational parameter.

15. The sensor system of embodiment 1, wherein: the metamaterial trackis configured to modify the first continuous wave based on a real-timevalue of the rotational parameter to be measured as the measurementvalue, thereby producing the first receive signal having the firstmeasurement unique to the real-time value of the rotational parameter.

16. The sensor system of embodiment 1, further comprising: a referencetrack mechanically coupled to the rotational axis and arranged at leastpartially around the rotational axis, and wherein the reference track isvoid of metamaterial, wherein the at least one transmitter is configuredto transmit a second continuous wave at the reference track thatproduces a reference signal from the second continuous wave, wherein theat least one quadrature continuous-wave receiver is configured toreceive the reference signal, acquire a second measurement of the firstproperty from the reference signal, and measure a distance to the firstmetamaterial track based on the second measurement.

17. The sensor system of embodiment 16, wherein the at least onequadrature continuous-wave receiver is configured to generate from thereference signal an in-phase demodulated signal and a quadraturedemodulated signal, use the in-phase demodulated signal and thequadrature demodulated signal to derive the second measurement, anddetermine the measurement value for the rotational parameter based onthe first and the second measurements.

18. The sensor system of embodiment 1, further comprising: a referencetrack mechanically coupled to the rotational axis and arranged at leastpartially around the rotational axis, wherein the at least onetransmitter is configured to transmit the first continuous wave at thereference track that is configured to produce a reference signal fromthe first continuous wave, wherein the at least one quadraturecontinuous-wave receiver is configured to generate from the referencesignal a reference in-phase demodulated signal and a referencequadrature demodulated signal, use the reference in-phase demodulatedsignal and the reference quadrature demodulated signal to derive asecond measurement of the first property from the reference signal, anddetermine the measurement value for the rotational parameter based onthe first and the second measurements.

19. The sensor system of embodiment 1, further comprising: furthercomprising a reference track mechanically coupled to the rotational axisand arranged at least partially around the rotational axis, wherein theat least one transmitter is configured to transmit a second continuouswave at the reference track that is configured to produce a referencesignal from the second continuous wave, wherein the at least onequadrature continuous-wave receiver is configured to generate from thereference signal a reference in-phase demodulated signal and a referencequadrature demodulated signal, use the reference in-phase demodulatedsignal and the reference quadrature demodulated signal to derive asecond measurement of the first property from the reference signal, anddetermine the measurement value for the rotational parameter based onthe first and the second measurements.

20. The sensor system of embodiment 19, wherein the first continuouswave is a monochromatic wave having a first frequency and the secondcontinuous wave is a monochromatic wave having a second frequencydifferent from the first frequency.

21. The sensor system of embodiment 20, wherein: the first metamaterialtrack has a first resonance bandwidth, and the first frequency is withinthe first resonance bandwidth and the second frequency is outside thefirst resonance bandwidth, and the reference track is made ofmetamaterial and has a second resonance bandwidth, and the firstfrequency is outside the second resonance bandwidth and the secondfrequency is inside the second resonance bandwidth.

22. The sensor system of embodiment 19, wherein: the first and thesecond continuous waves are monochromatic waves having a same frequency,and the at least one quadrature continuous-wave receiver is configuredto calculate a difference between the first measurement and the secondmeasurement, and determine measurement value of the rotational parameterof the rotational shaft based on the difference.

23. The sensor system of embodiment 22, the first metamaterial track hasa first resonance bandwidth and the second metamaterial track has asecond resonance bandwidth different from the first resonance bandwidth.

24. A method of determining a rotational parameter of a rotatable shaft,the method comprising: transmitting a first continuous wave towards afirst metamaterial track mechanically coupled to the rotatable shaft;converting, by the first metamaterial track, the first continuous waveinto a first receive signal based on a real-time value of the rotationalparameter; receiving, by a quadrature continuous-wave receiver, thefirst receive signal; acquiring, by the quadrature continuous-wavereceiver, a first measurement of a first property of the first receivesignal; and determining, by the quadrature continuous-wave receiver,determine the real-time value of the rotational parameter of therotational shaft based on the first measurement.

25. A rotation sensor system, comprising: a rotational shaft configuredto rotate about a rotational axis; a first array of millimeter-wave(mm-wave) structures mechanically coupled to the rotational shaft,wherein the first array of mm-wave structures is arranged at leastpartially around the rotational axis, and wherein the first array ofmm-wave structures has a first working resonance frequency; a secondarray of mm-wave structures mechanically coupled to the rotationalshaft, wherein the second array of mm-wave structures is arranged atleast partially around the rotational axis, and wherein the second arrayof mm-wave structures has a second working resonance frequency that isdifferent from the first working resonance frequency; at least onetransmitter configured to transmit a first electro-magnetic transmitsignal towards the first array of mm-wave structures and transmit asecond electro-magnetic transmit signal towards the second array ofmm-wave structures, wherein the first array of mm-wave structures isconfigured to convert the first electro-magnetic transmit signal into afirst electro-magnetic receive signal, wherein the second array ofmm-wave structures is configured to convert the second electro-magnetictransmit signal into a second electro-magnetic receive signal; and atleast one receiver configured to receive the first electro-magneticreceive signal and the second electro-magnetic receive signal, determinea first rotational parameter of the rotational shaft based on the firstelectro-magnetic receive signal, and determine a second rotationalparameter of the rotational shaft based on the second electro-magneticreceive signal, wherein the first rotational parameter and the secondrotational parameter are different rotational parameters.

26. The rotation sensor system of embodiment 25, wherein: the firstrotational parameter is a rotational speed of the rotational shaft, anabsolute angular position of the rotational shaft, a rotation directionof the rotational shaft, or a torque applied to the rotational shaft,and the second rotational parameter is the rotational speed of therotational shaft, the absolute angular position of the rotational shaft,the rotation direction of the rotational shaft, or the torque applied tothe rotational shaft.

27. The rotation sensor system of embodiment 25, wherein the first arrayof mm-wave structures has at least one characteristic that changes alonga length of the first array of mm-wave structures such that a singleperiod of characteristic change is encoded along the length of the firstarray of mm-wave structures.

28. The rotation sensor system of embodiment 25, wherein the first arrayof mm-wave structures is spatially separated from the second array ofmm-wave structures.

29. The rotation sensor system of embodiment 25, wherein the first arrayof mm-wave structures and the second array of mm-wave structures arespatially intermixed.

30. The rotation sensor system of embodiment 25, further comprising: athird array of mm-wave structures mechanically coupled to the rotationalshaft, wherein the third array of mm-wave structures is arranged atleast partially around the rotational axis, and wherein the third arrayof mm-wave structures has a third working resonance frequency that isdifferent from the first and the second working resonance frequencies;wherein the at least one transmitter is configured to transmit a thirdelectro-magnetic transmit signal towards the third array of mm-wavestructures, wherein the third array of mm-wave structures is configuredto convert the third electro-magnetic transmit signal into a thirdelectro-magnetic receive signal; and wherein the at least one receiveris configured to receive the third electro-magnetic receive signal, anddetermine a third rotational parameter of the rotational shaft based onthe third electro-magnetic receive signal, wherein the third rotationalparameter is different from the first and the second rotationalparameters.

31. The rotation sensor system of embodiment 25, further comprising: athird array of mm-wave structures mechanically coupled to the rotationalshaft, wherein the third array of mm-wave structures is arranged atleast partially around the rotational axis, and wherein the third arrayof mm-wave structures has a third working resonance frequency that isdifferent from the first and the second working resonance frequencies;wherein the at least one transmitter is configured to transmit a thirdelectro-magnetic transmit signal towards the third array of mm-wavestructures, wherein the third array of mm-wave structures are configuredto convert the third electro-magnetic transmit signal into a thirdelectro-magnetic receive signal; and wherein the at least one receiveris configured to receive the third electro-magnetic receive signal, anddetermine the second rotational parameter of the rotational shaft basedon second the and the third electro-magnetic receive signals, whereinthe second rotational parameter is the rotation direction.

32. The rotation sensor system of embodiment 25, further comprising: athird array of mm-wave structures mechanically coupled to the rotatableshaft, wherein the third array of mm-wave structures is arranged atleast partially around the rotational axis, and wherein the third arrayof mm-wave structures has the first working resonance frequency, whereinthe first array of mm-wave structures and the third array of mm-wavestructures are mutually coupled to each other by a torque dependentcoupling, thereby forming a mutually coupled structure that is sensitiveto a torque dependent angular shift between the first array of mm-wavestructures and the third array of mm-wave structures, wherein themutually coupled structure is configured to convert the firstelectro-magnetic transmit signal into the first electro-magnetic receivesignal based on a torque applied to the rotational shaft that causes thetorque dependent angular shift, the torque applied to the rotationalshaft being the first rotational parameter of the rotational shaft.

33. The rotation sensor system of embodiment 25, wherein a bandwidth ofthe second working resonance frequency does not overlap with a bandwidthof the first working resonance frequency.

34. The rotation sensor system of embodiment 33, wherein the firstelectro-magnetic transmit signal has a first frequency bandwidth thatoverlaps with the bandwidth of the first working resonance frequency butnot with the bandwidth of the second working resonance frequency, andthe second electro-magnetic transmit signal has a second frequencybandwidth that overlaps with the bandwidth of the second workingresonance frequency but not with the bandwidth of the first workingresonance frequency.

35. A rotation sensor system, comprising: a rotational shaft configuredto rotate about a rotational axis; a first array of millimeter-wave(mm-wave) structures mechanically coupled to the rotational shaft,wherein the first array of mm-wave structures is arranged at leastpartially around the rotational axis, and wherein the first array ofmm-wave structures has a first working resonance frequency; a secondarray of mm-wave structures mechanically coupled to the rotationalshaft, wherein the second array of mm-wave structures is arranged atleast partially around the rotational axis, and wherein the second arrayof mm-wave structures has a second working resonance frequency that isdifferent from the first working resonance frequency; a transmitterconfigured to transmit an electro-magnetic transmit signal towards thefirst array of mm-wave structures and the second array of mm-wavestructures, wherein the first array of mm-wave structures is configuredto convert the electro-magnetic transmit signal into a firstelectro-magnetic receive signal and the second array of mm-wavestructures is configured to convert the electro-magnetic transmit signalinto a second electro-magnetic receive signal; and at least one receiverconfigured to receive the first electro-magnetic receive signal and thesecond electro-magnetic receive signal, determine a first rotationalparameter of the rotational shaft based on the first electro-magneticreceive signal, and determine a second rotational parameter of therotational shaft based on the second electro-magnetic receive signal,wherein the first rotational parameter and the second rotationalparameter are different rotational parameters.

36. A linear movement sensor system, comprising: a linear movable targetobject configured to move linearly in a linear moving direction; a firstarray of millimeter-wave (mm-wave) structures coupled to the linearmovable target object, wherein the first array of mm-wave structuresextends along the linear moving direction, and wherein the first arrayof mm-wave structures has a first working resonance frequency; a secondarray of mm-wave structures coupled to the linear movable target object,wherein the second array of mm-wave structures extends along the linearmoving direction, and wherein the second array of mm-wave structures hasa second working resonance frequency that is different from the firstworking resonance frequency; at least one transmitter configured totransmit at least one electro-magnetic transmit signal towards the firstarray of mm-wave structures and the second array of mm-wave structures,wherein the first array of mm-wave structures is configured to convertone of the at least one electro-magnetic transmit signal into a firstelectro-magnetic receive signal and the second array of mm-wavestructures is configured to convert one of the at least oneelectro-magnetic transmit signal into a second electro-magnetic receivesignal; and at least one receiver configured to receive the first andthe second electro-magnetic receive signals, determine a first linearmovement parameter of the linear movable target object based on thefirst electro-magnetic receive signal, and determine a second linearmovement parameter of the linear movable target object based on thesecond electro-magnetic receive signal, wherein the first linearmovement parameter and the second linear movement parameter aredifferent linear movement parameters.

37. The linear position sensor system of embodiment 36, wherein: thefirst linear movement parameter is a linear speed, a movement direction,or an absolute linear position of the linear movable target object, andthe second linear movement parameter is the linear speed, the movementdirection, or the absolute linear position of the linear movable targetobject.

While various embodiments have been disclosed, it will be apparent tothose skilled in the art that various changes and modifications can bemade which will achieve some of the advantages of the concepts disclosedherein without departing from the spirit and scope of the invention. Itis to be understood that other embodiments may be utilized andstructural or logical changes may be made without departing from thescope of the present invention. It should be mentioned that featuresexplained with reference to a specific figure may be combined withfeatures of other figures, even in those not explicitly mentioned. Suchmodifications to the general inventive concept are intended to becovered by the appended claims and their legal equivalents.

With regard to the various functions performed by the components orstructures described above (assemblies, devices, circuits, systems,etc.), the terms (including a reference to a “means”) used to describesuch components are intended to correspond, unless otherwise indicated,to any component or structure that performs the specified function ofthe described component (i.e., that is functionally equivalent), even ifnot structurally equivalent to the disclosed structure that performs thefunction in the exemplary implementations of the invention illustratedherein. Thus, it will be obvious to those reasonably skilled in the artthat other components performing the same functions may be suitablysubstituted

Furthermore, the following claims are hereby incorporated into thedetailed description, where each claim may stand on its own as aseparate example embodiment. While each claim may stand on its own as aseparate example embodiment, it is to be noted that—although a dependentclaim may refer in the claims to a specific combination with one or moreother claims—other example embodiments may also include a combination ofthe dependent claim with the subject matter of each other dependent orindependent claim. Such combinations are proposed herein unless it isstated that a specific combination is not intended. Furthermore, it isintended to include also features of a claim to any other independentclaim even if this claim is not directly made dependent on theindependent claim.

It is further to be noted that methods disclosed in the specification orin the claims may be implemented by a device having means for performingeach of the respective acts of these methods. For example, thetechniques described in this disclosure may be implemented, at least inpart, in hardware, software, firmware, or any combination thereof,including any combination of a computing system, an integrated circuit,and a computer program on a non-transitory computer-readable recordingmedium. For example, various aspects of the described techniques may beimplemented within one or more processors, including one or moremicroprocessors, DSPs, ASICs, or any other equivalent integrated ordiscrete logic circuitry, as well as any combinations of suchcomponents.

Further, it is to be understood that the disclosure of multiple acts orfunctions disclosed in the specification or in the claims may not beconstrued as to be within the specific order. Therefore, the disclosureof multiple acts or functions will not limit these to a particular orderunless such acts or functions are not interchangeable for technicalreasons. Furthermore, in some embodiments, a single act may include ormay be broken into multiple sub acts. Such sub acts may be included andpart of the disclosure of this single act unless explicitly excluded.

What is claimed is:
 1. A rotation sensor system, comprising: arotational shaft configured to rotate about a rotational axis; a firstarray of millimeter-wave (mm-wave) structures mechanically coupled tothe rotational shaft, wherein the first array of mm-wave structures isarranged at least partially around the rotational axis, and wherein thefirst array of mm-wave structures has a first working resonancefrequency; a second array of mm-wave structures mechanically coupled tothe rotational shaft, wherein the second array of mm-wave structures isarranged at least partially around the rotational axis, and wherein thesecond array of mm-wave structures has a second working resonancefrequency that is different from the first working resonance frequency;at least one transmitter configured to transmit a first electro-magnetictransmit signal towards the first array of mm-wave structures andtransmit a second electro-magnetic transmit signal towards the secondarray of mm-wave structures, wherein the first array of mm-wavestructures is configured to convert the first electro-magnetic transmitsignal into a first electro-magnetic receive signal, and wherein thesecond array of mm-wave structures is configured to convert the secondelectro-magnetic transmit signal into a second electro-magnetic receivesignal; and at least one receiver configured to receive the firstelectro-magnetic receive signal and the second electro-magnetic receivesignal, determine a first rotational parameter of the rotational shaftbased on the first electro-magnetic receive signal, and determine asecond rotational parameter of the rotational shaft based on the secondelectro-magnetic receive signal, wherein the first rotational parameterand the second rotational parameter are different rotational parameters.2. The rotation sensor system of claim 1, wherein: the first rotationalparameter is a rotational speed of the rotational shaft, an absoluteangular position of the rotational shaft, a rotation direction of therotational shaft, or a torque applied to the rotational shaft, and thesecond rotational parameter is the rotational speed of the rotationalshaft, the absolute angular position of the rotational shaft, therotation direction of the rotational shaft, or the torque applied to therotational shaft.
 3. The rotation sensor system of claim 1, wherein thefirst array of mm-wave structures has at least one characteristic thatchanges along a length of the first array of mm-wave structures suchthat a single period of characteristic change is encoded along thelength of the first array of mm-wave structures.
 4. The rotation sensorsystem of claim 1, wherein the first array of mm-wave structures isspatially separated from the second array of mm-wave structures.
 5. Therotation sensor system of claim 1, wherein the first array of mm-wavestructures and the second array of mm-wave structures are spatiallyintermixed.
 6. The rotation sensor system of claim 1, furthercomprising: a third array of mm-wave structures mechanically coupled tothe rotational shaft, wherein the third array of mm-wave structures isarranged at least partially around the rotational axis, and wherein thethird array of mm-wave structures has a third working resonancefrequency that is different from the first working resonance frequencyand the second working resonance frequency; wherein the at least onetransmitter is configured to transmit a third electro-magnetic transmitsignal towards the third array of mm-wave structures, wherein the thirdarray of mm-wave structures is configured to convert the thirdelectro-magnetic transmit signal into a third electro-magnetic receivesignal; and wherein the at least one receiver is configured to receivethe third electro-magnetic receive signal, and determine a thirdrotational parameter of the rotational shaft based on the thirdelectro-magnetic receive signal, wherein the third rotational parameteris different from the first rotational parameter and the secondrotational parameter.
 7. The rotation sensor system of claim 1, furthercomprising: a third array of mm-wave structures mechanically coupled tothe rotational shaft, wherein the third array of mm-wave structures isarranged at least partially around the rotational axis, and wherein thethird array of mm-wave structures has a third working resonancefrequency that is different from the first working resonance frequencyand the second working resonance frequency; wherein the at least onetransmitter is configured to transmit a third electro-magnetic transmitsignal towards the third array of mm-wave structures, wherein the thirdarray of mm-wave structures are configured to convert the thirdelectro-magnetic transmit signal into a third electro-magnetic receivesignal; and wherein the at least one receiver is configured to receivethe third electro-magnetic receive signal, and determine the secondrotational parameter of the rotational shaft based on the second and thethird electro-magnetic receive signals, wherein the second rotationalparameter is a rotation direction of the rotational shaft.
 8. Therotation sensor system of claim 1, further comprising: a third array ofmm-wave structures mechanically coupled to the rotatable shaft, whereinthe third array of mm-wave structures is arranged at least partiallyaround the rotational axis, and wherein the third array of mm-wavestructures has the first working resonance frequency, wherein the firstarray of mm-wave structures and the third array of mm-wave structuresare mutually coupled to each other by a torque dependent coupling,thereby forming a mutually coupled structure that is sensitive to atorque dependent angular shift between the first array of mm-wavestructures and the third array of mm-wave structures, wherein themutually coupled structure is configured to convert the firstelectro-magnetic transmit signal into the first electro-magnetic receivesignal based on a torque applied to the rotational shaft that causes thetorque dependent angular shift, the torque applied to the rotationalshaft being the first rotational parameter of the rotational shaft. 9.The rotation sensor system of claim 1, wherein a bandwidth of the secondworking resonance frequency does not overlap with a bandwidth of thefirst working resonance frequency.
 10. The rotation sensor system ofclaim 9, wherein the first electro-magnetic transmit signal has a firstfrequency bandwidth that overlaps with the bandwidth of the firstworking resonance frequency but not with the bandwidth of the secondworking resonance frequency, and the second electro-magnetic transmitsignal has a second frequency bandwidth that overlaps with the bandwidthof the second working resonance frequency but not with the bandwidth ofthe first working resonance frequency.
 11. A rotation sensor system,comprising: a rotational shaft configured to rotate about a rotationalaxis; a first array of millimeter-wave (mm-wave) structures mechanicallycoupled to the rotational shaft, wherein the first array of mm-wavestructures is arranged at least partially around the rotational axis,and wherein the first array of mm-wave structures has a first workingresonance frequency; a second array of mm-wave structures mechanicallycoupled to the rotational shaft, wherein the second array of mm-wavestructures is arranged at least partially around the rotational axis,and wherein the second array of mm-wave structures has a second workingresonance frequency that is different from the first working resonancefrequency; a transmitter configured to transmit an electro-magnetictransmit signal towards the first array of mm-wave structures and thesecond array of mm-wave structures, wherein the first array of mm-wavestructures is configured to convert the electro-magnetic transmit signalinto a first electro-magnetic receive signal and the second array ofmm-wave structures is configured to convert the electro-magnetictransmit signal into a second electro-magnetic receive signal; and atleast one receiver configured to receive the first electro-magneticreceive signal and the second electro-magnetic receive signal, determinea first rotational parameter of the rotational shaft based on the firstelectro-magnetic receive signal, and determine a second rotationalparameter of the rotational shaft based on the second electro-magneticreceive signal, wherein the first rotational parameter and the secondrotational parameter are different rotational parameters.
 12. Therotation sensor system of claim 11, wherein: the first rotationalparameter is a rotational speed of the rotational shaft, an absoluteangular position of the rotational shaft, a rotation direction of therotational shaft, or a torque applied to the rotational shaft, and thesecond rotational parameter is the rotational speed of the rotationalshaft, the absolute angular position of the rotational shaft, therotation direction of the rotational shaft, or the torque applied to therotational shaft.
 13. The rotation sensor system of claim 11, whereinthe first array of mm-wave structures has at least one characteristicthat changes along a length of the first array of mm-wave structuressuch that a single period of characteristic change is encoded along thelength of the first array of mm-wave structures.
 14. The rotation sensorsystem of claim 11, wherein the first array of mm-wave structures isspatially separated from the second array of mm-wave structures.
 15. Therotation sensor system of claim 11, wherein the first array of mm-wavestructures and the second array of mm-wave structures are spatiallyintermixed.
 16. The rotation sensor system of claim 11, furthercomprising: a third array of mm-wave structures mechanically coupled tothe rotational shaft, wherein the third array of mm-wave structures isarranged at least partially around the rotational axis, and wherein thethird array of mm-wave structures has a third working resonancefrequency that is different from the first working resonance frequencyand the second working resonance frequency, wherein the third array ofmm-wave structures is configured to convert the electro-magnetictransmit signal into a third electro-magnetic receive signal, andwherein the at least one receiver is configured to receive the thirdelectro-magnetic receive signal, and determine a third rotationalparameter of the rotational shaft based on the third electro-magneticreceive signal, wherein the third rotational parameter is different fromthe first rotational parameter and the second rotational parameter. 17.The rotation sensor system of claim 11, further comprising: a thirdarray of mm-wave structures mechanically coupled to the rotationalshaft, wherein the third array of mm-wave structures is arranged atleast partially around the rotational axis, and wherein the third arrayof mm-wave structures has a third working resonance frequency that isdifferent from the first working resonance frequency and the secondworking resonance frequency, wherein the third array of mm-wavestructures are configured to convert the electro-magnetic transmitsignal into a third electro-magnetic receive signal, and wherein the atleast one receiver is configured to receive the third electro-magneticreceive signal, and determine the second rotational parameter of therotational shaft based on the second and the third electro-magneticreceive signals, wherein the second rotational parameter is a rotationdirection of the rotational shaft.
 18. The rotation sensor system ofclaim 11, further comprising: a third array of mm-wave structuresmechanically coupled to the rotatable shaft, wherein the third array ofmm-wave structures is arranged at least partially around the rotationalaxis, and wherein the third array of mm-wave structures has the firstworking resonance frequency, wherein the first array of mm-wavestructures and the third array of mm-wave structures are mutuallycoupled to each other by a torque dependent coupling, thereby forming amutually coupled structure that is sensitive to a torque dependentangular shift between the first array of mm-wave structures and thethird array of mm-wave structures, and wherein the mutually coupledstructure is configured to convert the electro-magnetic transmit signalinto the first electro-magnetic receive signal based on a torque appliedto the rotational shaft that causes the torque dependent angular shift,the torque applied to the rotational shaft being the first rotationalparameter of the rotational shaft.
 19. The rotation sensor system ofclaim 11, wherein a bandwidth of the second working resonance frequencydoes not overlap with a bandwidth of the first working resonancefrequency.
 20. A linear movement sensor system, comprising: a linearmovable target object configured to move linearly in a linear movingdirection; a first array of millimeter-wave (mm-wave) structures coupledto the linear movable target object, wherein the first array of mm-wavestructures extends along the linear moving direction, and wherein thefirst array of mm-wave structures has a first working resonancefrequency; a second array of mm-wave structures coupled to the linearmovable target object, wherein the second array of mm-wave structuresextends along the linear moving direction, and wherein the second arrayof mm-wave structures has a second working resonance frequency that isdifferent from the first working resonance frequency; at least onetransmitter configured to transmit at least one electro-magnetictransmit signal towards the first array of mm-wave structures and thesecond array of mm-wave structures, wherein the first array of mm-wavestructures is configured to convert one of the at least oneelectro-magnetic transmit signal into a first electro-magnetic receivesignal and the second array of mm-wave structures is configured toconvert one of the at least one electro-magnetic transmit signal into asecond electro-magnetic receive signal; and at least one receiverconfigured to receive the first electro-magnetic receive signal and thesecond electro-magnetic receive signal, determine a first linearmovement parameter of the linear movable target object based on thefirst electro-magnetic receive signal, and determine a second linearmovement parameter of the linear movable target object based on thesecond electro-magnetic receive signal, wherein the first linearmovement parameter and the second linear movement parameter aredifferent linear movement parameters.
 21. The linear movement sensorsystem of claim 20, wherein: the first linear movement parameter is alinear speed, a movement direction, or an absolute linear position ofthe linear movable target object, and the second linear movementparameter is the linear speed, the movement direction, or the absolutelinear position of the linear movable target object.